Pre-Columbian Ring Ditches along the Yacunta and Rapulo Rivers, Beni, Bolivia: A Prelintinary RevieW

8/11/2019 Pre-Columbian Ring Ditches along the Yacunta and Rapulo Rivers, Beni, Bolivia: A Prelintinary RevieW

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413

Pre-Coluntbian Ring Ditches along the

Yacunta and Rapulo Rivers, Beni,

Bolivia: A Prelintinary RevieW"

John H. Walker

University of Central Florida

Orlando, Florida

Arawak speakers have been of interest to missionaries

and historians for more than 300 years, although they were

always one of many linguistic groups in Mojos. William M.

Denevan and David Block agree that contact with and con-

version of Arawal( speakers was the highest priority for Je-

suit missionaries, and their reviews of the documents sug-

gest that Arawal( speal(ers were a minority in Mojos at the

time of contact (Block 1994; Denevan 1966). Denevan ar-

gues for geographic continuity: "Nevertheless, most of the

tribes surviving in the Beni are still found in the general

area where they first were encountered by the Spaniards"

(1966: 40). The areas inhabited by the Arawal(-spealcing

Mojo and Baure groups have many pre-Columbian earth-

works, but so does non-Arawak Movima and Cayuvava

territory. Therefore, there is no direct spatial correspon-

dence between pre-Columbian earthworks and contact pe-riod Arawak speakers. If there was a link between Arawak

speakers and the construction and use of earthworks such

as raised fields or ring ditches, that link must be more com-

plex than a simple spatial correspondence.

Pre-Columbian farmers built a variety of earthworks in the Llanos de Mojos) part of the

Bolivian Amazon. Raised fields) canals) causeways) and mounds of various types in this

region date to ca. 800 B.G-A.D. 1600. In centralMojos) archaeological work was carried

out along the Yacuma) a lawe west-bank tributary of the Mamore River. Four ring ditches

and two areas of associated raised agricultural fields were mapped. The Global PositioningSystem was used to document earthworks under the forest canopy which were analyzed with-

in a Geographic Information System. Ceramic evidence is also included. The r ing ditches in

this study expand the known range of such earthworks in Mojos by 200 km. This revised dis-

tribution of ring ditches changes interpretations of the long-term history ofArawak speakers

in Mojos and throughout Amazonia. While earthworks in Mojos clearly represent systems of

intensive agriculture) they cannot be associated only with Arawak speakers or with Arawak

languages.

Introduction

The ring ditch is a type of pre-Columbian earthwork

found in eastern Bolivia often interpreted as evidence of

cultural development and population movement in Ama-

zonian archaeology. It has been widely known since the

1960s that agricultural societies built earthen mounds,

raised fields, canals, and causeways in the Bolivian Ama-

zan. The Llanos de Mojos (or Mojos), a seasonally flood-

ed tropical savanna, covers more than 90,000 sq km (with

an additional 20,000 sq km of interspersed forest), and

many types of earthworks have been documented

(Denevan 1966; Hanagarth 1993; FIG. I). This paper ex-

tends the documented range of ring ditches across the

MamonS River to the west. Ring ditches in this area were

found in association with large raised fields, unlike in the

east where they were first described. Ring ditches are partof a complex of material traits attributed to Arawal( speal(-

ing peoples. Ring ditches are sometimes presented as evi-

dence of a history and prehistory of Arawal( expansion

(Heckenberger 2005) or of a system of long-distance trade

(Hornborg 2005). The extension of the geographic range

where these features are found, however, leads to a ques-

tioning of these links. The wide variety of language groups

and languages present in Mojos mal(es it difficult to estab-

lish a direct relationship between Arawal( speakers and ring

ditches.

Previous Archaeological Research

Not as well studied as the Bolivian Altiplano, Llanos de

Mojos is nonetheless better known than many places in the

Amazon. Previous research has described a wide range of

earthworks, including mounds, forest islands, and ring


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414 Pr e-Columbian Ring Ditches along the Yacuma and Rapulo Rivers) Beni) BoliviajWalkeJl'

Central Amazon

Brazil

Madeira River Basin

c::===::J10 km

o 1 25 2 50 1000 km

reservoirs. Ring ditches, mounds, and forest islands are dif-

ferent manifestations of similar processes, rather than dis-

tinct phenon1ena. Their relationship to landscapes of raised

fields, burials, and ceramics is more significant than the

form of the mound or ditch. Ring ditches in the Llanos de

Mojos are described by Denevan (1966, 2001) and in

greater detail by Erickson (Erickson 2006a). Similar fea-

tures have also been reported fron1 Brazil (Heckenberger

2005; Wust and Barreto 1999).

The first published inforn1ation about ring ditches in

Mojos dates to the 1960s. Denevan distinguished between

ring ditches east of the Man10re River and those to the

west (1966: 61-64). East of the river, near the modern

town of Baures are circular ditches associated with the

Baure people. The ethnohistoric Baures built palisaded vil-

lages, some of which had associated ring ditches. Ethno-

graphic accounts also describe moated villages among the

Canichana east of the Mamore and about 100 km NE of the

mouth of the Yacuma. Denevan also notes that mounds

west of the Mamore are often closely associated with "bor-

50Q 750

Figure 1. The location of the Llanos de Iv10jos within the Madeira River Basin, between the Andes moun-

tains, Central Amazon, Brazilian highlands, and the Gran Chaco. The detail map to the right shows the

Yacuma and Rapulo rivers, on the west bank of the Mamore River, with the location of the four ring

ditches: 1) Estancita Island; 2) San Francisco Island; 3) San Pablo Island; and 4) Zap una Island.

ditches (Denevan 1966; Erickson 2006a; Walker 2008).

Ring ditches are part of a continuum of types of earth-

works associated \vith occupation, ranging from large

n10unds that cover tens of hectares and are higher than 9

m, to isolated forest islands less than 100 m across, and less

than 1 m tall. Mojos first attracted the attention of foreign

archaeologists when Erland N ordenskiold excavated a se-

ries of large mounds to the south and east of Trinidad

(Nordenskiold 1913). Prlin1ers' ongoing excavations of

large mounds in SE Mojos confirm that these locations

were occupied by large numbers of people, and that a so-

phisticated burial tradition was maintained (Prumers

2000, 2001, 2002). Many of these mounds contain urn

burials and may have had more than one purpose.

Forest islands comprise another type of evidence of oc-

cupation. For example, along the lruyafiez River, forest is-

lands (larger than 45 m in diameter) were occupied in

seven out of eight investigated cases (Walker 2004). Al-

though these islands were not surrounded b ring ditches,

several were associated with large borrow pits or water


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row pits;' a consequence of their artificial construction.

Denevan contrasts these two types of earthworks with true

ring ditches found only east of the Mamore River.

Clark L. Erickson, from 1995 to the present, has ex-

plored and described ring ditches and other earthworks in

the eastern half of Mojos. This area includes ring ditches,

long causeways, and shorter, "zig-zag" causeways (Erick-

son 2006a). Although he argues that many different inter-

pretations of ring ditches are possible, Erickson concludes

that they probably represent occupation. The first field re-

port describes eight ring ditches ranging between 1 and 4

ha (Erickson, personal communication 1997). They are of-

ten clearly marked and well preserved, with ditches as deep

as 2 or 3 m. Ditches can be circular, oval, octagonal, or D-

shaped. They are fairly evenly distributed between forest

and areas where the forest has been cut for pasture or con-

struction and many ring ditches are found directly beneathmodern occupation. Erickson argues that ring ditches

probably had a defensive function (2006a: 258-260).

As part of a pilot project to recover and interpret ar-

chaeologicallandscapes in the YacumaRiver basin, we con-

ducted a brief reconnaissance and limited survey in June

2007, centered on the town of Santa Ana del Yacuma. The

goal of this ongoing research project is to recover spatial

patterns of landscape features (including raised fields and

ring ditches) and relate them to patterns of social organi-

zation using Geographic Information Systems (GIS), Ge-

ographic Positioning Systems (GPS), and the Internet to

publish and analyze the results.

Methods

Four different methods were used to record and map

ring ditches. First, Advanced Spaceborne Thermal Emis-

sion and Reflection Radiometer (ASTER) satellite imagery

was analyzed in conjunction with GPS data to guide field

survey. Second, earthworks and other surface features were

mapped using the GPS. Third, ceramics were collected

from visible surface scatters. Finally, the ceramics were de-

scribed using a modal analysis.

An image produced from Visible and Near Infra-Red

(VNIR) ASTER data in conjunction with the GPS guidedthe reconnaissance. This image has a resolution of 15 m,

and the 14 available bands can be classified and used to rep-

resent different types of land cover (Aronoff2005: 185). It

is possible to distinguish individual raised fields in some

cases, as well as narrow cattle trails, fences, and other small

features.

Before survey and mapping began, we completed a gen-

eral reconnaissance of the area on a motorcycle, using GPS

to map reference points such as crossroads, fences, ranch-

es' small bridges, and spillways. These latter features,

Jour nal ofFieldArcha eologyjVol. 33)2008 415

which tal(e the form of metal tubes with compacted soil

over them, are informative because they correspond to

places where water is lil(ely to cover the road during the

wet season. Centered on the town of Santa Ana del

Yacuma, the total area accessible by road within a single

day during the dry season is larger than 50 sq km. In the

course of this reconnaissance, some small islands (cut by

the public road) were registered. In the case of Primera

Island, a surface collection was tal(en. This island is ap-

proximately 100 m in diameter, with very little relief com-

pared to the surrounding pampa. Surface ceramics confirm

the relationship between forest islands and occupation.

Other islands included Muerto Island and Paquio Island,

where ceramics were not found. The mapping process was

reserved for the larger islands.

A Garmin GPS with an antenna that permits reception

underneath forest vegetation and inside buildings was usedfor mapping. The mean error of the readings is easily dis-

played and continuously updated and it is possible to mark

a location using the average of many readings. Waypoints

usually had an error of less than 4 m, and often less than 3

m. Even though this particular receiver has many advan-

tages, all of the mapping described here could be under-

tal(en with a more basic (and less expensive) unit, with the

possible exception of mapping earthworks underneath

thick forest cover. Waypoints and tracks were downloaded

to a laptop computer and verified every day.

Combining GPS and ASTER data, it was possible to lo-

cate features in the field that are visible on the ASTER im-age. For example, at San Pablo a forest island was located

with a point marked on the computer screen, using the

ASTER image. With the GPS in the field it was easy to nav-

igate to this point, even though the same forest island had

previously been missed during an unaided ground search.

The accuracy and precision of the GPS enabled the map-

ping of ring ditches and large raised fields. Ring ditches

were mapped by talcing GPS points while wallcing the cir-

cumference of the ditch and recording notes on its charac-

teristics. For raised fields, maps were produced by wallcing

along the boundaries of raised field platforms, defined as

the transition between the uneven savanna and the flat sur-face of the platform. The points continuously and auto-

matically recorded by the GPS made this simple. In many

cases, it was difficult to determine the boundaries of the

platform, usually because of the passage of cattle, or be-

cause of the construction of roads or airstrips. The com-

parison of results from GPS mapping under varying con-

ditions showed that the accuracy was sufficient for the pur-

poses of this study. It took less than 15 minutes to map a

large raised field platform, and about an hour to map a ring

ditch.


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416 Pr e-Columbian Ring Ditches along the Yacuma and Rapulo Rivers) Beni) BoliviajW"alker

X

Treefalls with no ceramics present

Xx

x

Circular pattern of low spots

x

x

Forest island

Figure 2. Scale drawing of earthworks at Estancita Island made from GPS points and track log. Black

points represent ceramics on the surface, white points are tree falls without evidence of ceramics, and

earthworks are represented b hatched lines.

Ceramics were collected from the surface in order to es-

tablish the presence or absence of occupation. Seven forest

islands were selected for surface collection on the basis of

associated earthworks and dry, high ground. Five of theselocations had ceramics on the surface. In total, nine ceram-

ic collections were taken from five different islands, total-

ing 53 sherds.

In general, it is difficult to fmd ceramics or other arti-

facts on the surface because of vegetation. In continuous

canopy forest and in arboledas (scrub forest), tree falls can

be inspected and used as "natural excavations;' because

they move large amounts of soil from as deep as 1.5 m

below the surface. Ceramics were collected from these, but

collection was limited to rimsherds and those with distinc-

tive surface treatments. The evidence from along the

Iruyafiez River supports the conclusion that there is astrong positive correlation between forest islands and

human occupation (Walker 2004). Along the Iruyafiez,

test excavations in forest islands, levees, and the savanna

showed that occupation was concentrated on levees and

forest islands. Although test excavations have not been car-

ried out in the savannas along the Yacuma, these results

suggest a similar correlation between dry forests and evi-

dence of occupation.

The ceramics were washed, photographed, curated, and

described using a modal analysis. Ceramic modes were di-

vided into five groups: clay, form, surface treatment, sur-

face polish, and design, and compared with previously es-

tablished ceramic typologies. It should be noted that the

development of ceramic typologies for Mojos is advancingslowly.

Ring Ditches

Four large forest islands were surveyed and mapped.

Each location is described here, along with associated bod-

ies of water, nearby raised fields, and the form of the ring

ditch or similar earthworks.

Estancita Island

Estancita Island (FIG. 2) is a forest island approximately

30.3 ha in area 3.7 km NNW of Santa Ana, on the east side

of the road north to Exaltaci6n. This island is used by cat-tle as a refuge during the wet season. Landowners report

that the 2007 inundation was particularly high along the

Mamore and Apere rivers, but apparently was not excep-

tional along the Yacuma and Rapulo. Estancita Island is

said by the landowner never to flood.

Just north of Estancita Island is a swamp (bajio or

curiche) that is part of a larger wetland between the Yacuma

and Omi rivers. This wetland is about 10 km long from the

western main body to a smalllal(e in the east. The ecotone

between swamp and forest island is a flooded forest. Al-


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Journal of Field ArchaeologyjVol.33) 2008 417

Raised fields

Raised fields

Forest islandsHigher

ground

ceramic

finds Ring ditch

Figure 3. Scale drawing of earthworks at San Francisco Island made from GPS points and track log. Black

points represent ceramics on the surface and hatched lines represent earthworks.

though heavily wooded, there is no other high ground in

this forest, which appears to have a different species com-

position than the dry forest of the island. Because of the

thick vegetation it was not possible to determine whether

raised fields are present between Estancita Island and theswamp, but raised fields are often found in such ecotones

between permanent wetlands and high ground.

Estancita Island has an irregular shape, broader to the

west and narrower to the east. On the south side of the is-

land's interior, a series of low spots form two-thirds of a cir-

cle about 160m across. These low spots are circular, be-

tween 5 and 15 m in diameter, and two are elongated,

along the perimeter of the circle. Their depth was not mea-

sured because of standing water, but the low spots are

probably between 1 and 2 m deep. The complete circle de-

fined by this arc has an area of 2.2 ha. The circle of low

spots is not well defined to the north, where a grove ofmotacu palms (Attalea phalerata) grows. The highest

ground on the island is found within this circle, and ce-

ramics were found in five different locations on the surface.

Outside the circle, a total of 13tree falls were examined,

none of which contained ceramics. Because of its semicir-

cular shape and the ceramics, this pattern of low spots is

clearly the result of intentional movement of earth.

San Fra ncisco Island

San Francisco Island (FIG. 3) is part of a group of four

forest islands on the property of the San Francisco ranch.

It has an area of approximately 2.7ha and is located 20m

west of the road between Santa Ana del Yacuma and San

Ignacio de Moxos.

The island is in an unusually wet area. To the north ofSan Francisco Island is a large arroyo or creek that origi-

nates in the pampa between the Yacuma and Rapulo rivers

and empties into the Yacuma near the port of San Loren-

zo. As with many creeks along the Yacuma, it is well de-

fined by forest vegetation close to its mouth, but farther

from the river (about 15 km) it is not marked by trees and

fans out into a broad wetland.

During initial reconnaissance, "large raised fields" as de-

fined by Denevan (1966: 85-87, 2001) were recognized

in the savanna to either side of the island (FIG. 4). Eight

platforms to the west and two platforms to the east were

mapped (TABLE I). These ten platforms are indistinguish-able from the large raised field platforms that are common

along the Iruyaiiez River north of this region (Wallcer

2000,2001,2004: 39). These platforms are well preserved

even though this location was a prosperous ranch for more

than 50 years and the savanna was consequently eroded by

the passage of many herds of cattle. In pre-Columbian

times San Francisco Island was associated with at least 4 ha

of large raised fields and probably a much larger area.

The island is rougWy circular, approximately 150m in

diameter. As is common, the boundary between forest and


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418 Pr e-Columbian Ring Ditches along the Yacuma and Rapulo Rivers) Beni) Bolivia/Walker

Figure 4. View of large raised fields, 400 mwest of S~U1Francisco Island.

Table 1. Dilnensions of raised fields

near San Francisco Island ll1easured

using the GPS.

"ring ditch." The ditch takes the form of a circular canal,

with a greater difference between the floor of the ditch and

the interior side than between the floor of the ditch and the

exterior side. It encloses an area of about 1.06 ha and varies

between 50 cm and 1 nl. in depth. Generally the ditch is

about 5 nl. across from level high ground to level high

ground. Because of its circular form and because of the ce-

ramics found within the ditch, it is clear that this is an in-

tentional construction.

Platftrm Length (m) Width (m)

1 231.41 18.912 178.03 13.193 268.70 19.284 277.39 13.375 351.02 15.126 285.97 17.297 222.70 16.408 171.36 10.91

9 200.40 19.1610 202.21 15.99Mean 238.92 15.96St. dey. 56.342 2.839

San Pablo Island

San Pablo Island (FIG. 5) is an oval-shaped island with

an area of about 15.6 ha. It is located directly alongside the

Rapulo River, on the property of the ranch of the same

nanle, about 7 Ian SE of the road between Santa Ana and

Nieves. The access road between the larger road and the

Chawisa ranch passes 450 m west of the island. San Pablo

savanna is not easy to define, but the contrast between

grasses and leaf litter as ground cover serves to distinguish

it. The earthwork found on this island is an unambiguous


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Jour nal ofField Archa eologyjVol.33) 2008 419

Forest island

Seasonal wetland

Rapulo

River

pond

Ring ditchI "

I I I200 meters

Figure 5. Scale drawing of earthworks at San Pablo Island made from GPS points and track log. Black

points represent ceralnics on the surface and hatched lines represent earthworks.

11.30 ha. The ditch is n10re difficult to see in the savanna,

an effect of differences in vegetation between the forest and

the savanna.

San Pablo is a clear example of a ring ditch, possibly

with hydraulic functions. In its SE corner, the ditch runs

outside the pond, leaving a narrow strip of higher ground

between. The ditch is most clearly defined next to the

river, and least clearly defined in the savanna. It is inter-

rupted by another low spot or pond at its westernmost

point. The ditch is connected to the river by a short, deep

channel that cuts through the river levee. Another shallow,

seasonal creek connects the ditch to the river on the south.

It appears that today water can pass from the savanna to the

west, through the ditch, and out to the river through each

of the two creeks. It is possible that this was the case in pre-

Columbian times as well.

Island is directly alongside the river and is located on top

of the high levee of the river. Large creeks empty into the

river about 1.5lU11south and 600 n1 NE of the island.

In the savanna to the west and south of the island large

raised fields are visible in tl1e ASTER image although they

could not be located on the ground. This savanna was not

recently burned or "clean" in June 2007, and it is possible

that the fields were not visible because of these conditions.

Continued analysis of the ASTER data, as well as aerial

photographs, will resolve this question.

The island has a truncated oval shape and is longer fron1

the NW to the SE than fron1 the NE to the sw. Southeast of

the island tl1e boundary is irregular, with a n1ix of savanna

and woods. There is a pond about 0.5 ha in extent on the

SE side of the island. Within the forest boundary but ex-

tending beyond it to the south and west is an oval-shaped

ring ditch (FIG. 6). Inside this ring tl1e elevation of the is-

land is approximately 3-4 m higher tl1an the surrounding

pampa. To tl1e east, nearer the river, the ditch is about 2 m

deep. To the wsw, farther from the river, the ditch is about

50cm deep. The ditch is approxin1ately 5 m wide tl1rough-

out its circumference, and it encloses an area of about

Zapund Island

Zapuna Island (FIG. 7) is triangular with an irregular

boundary, mixing savanna and woods, especially on its

south side. Zapuna is the largest of the four islands, be-

tween 28 and 35 ha (depending on where the forest


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420 Pre-Columbian Ring Ditches along the Yacuma and Rapulo Riversy Beniy BoliviajWalker

Figure 6. View of the ring ditch at San Pablo Island.

boundary is drawn). Zapuna is located in the center of the

large savanna between the Rapulo and Apere rivers. It is

the westernmost of a group of four large islands that con-

tinue to the north and east. Although it was possible to cir-

cumnavigate the island, due to time the interior of the

island was mapped only north of the fence. A large, well-

defined swamp bounded Zapuna Island to the west. The

contrast between the swamp and the elevation of the island

is notable. The island is at least 3 m higher than its sur-

roundings.

In the savanna east of the island, large raised fields are

visible on the ASTER image. These fields are located on the

property of the neighboring ranch and we did not reach

them on foot, though they are clearly visible from the air.

The presence of forest islands and large raised fields makes

this area similar to the savanna near San Francisco and San

Pablo islands: Zapuna Island is also associated with large

raised fields.

Three large low spots were mapped within the north

half of the forest on the island. These low spots do not con-

nect to fonn a circular ditch, but surround the highest

points within the island and rougWy correspond to the car-

dinal directions. The low spots are approximately 10 ill in

dialneter and may be as deep as 2 or 3 m. The area within

the circle defined by these low spots is higher than the area

outside. This mound is between 7 and 11 ha, with 10

hectares being the most likely figure. This island is notice-

ably higher than the other examples outside of the study

area and in comparison with others throughout Mojos it

may more properly be called a mound. Based on the ce-

ramics collected from within the circle, it is likely that these

depressions were intentionally created, but it is difficult to

tell without surveying the south half of the island.

Ceramics

Fifty-three potsherds were collected from five locations.

Clays range from poorly-fired to well-fired and occur in a

variety of colors. Brown, gray, light brown, tan, and buff

are all conlmon. All sherds have a gray center and are in-

completely fired. Grog is the most conl1non temper, and

there is one example of shell temper. Notable by its absence

is sponge temper (or cauxi), which is well-known from


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Figure 7. Scale drawing of earthworks at Zapuna Island made from GPS points and track log. Black

points represent ceramics on the surface and hatched lines represent earthworks.

many Amazonian contexts. Some fragments have a

smooth, powdery surface that is almost soapy.Vessel forms are poorly known, although some can be

partially reconstructed. From the San Pablo ring ditch

there is one example of a grinder (ormoleador, FIG. 8). Sev-

eral vessels (probably jars) have slightly flaring lips. Some

of these rims are flattened and others are curved. There is

one example of a carinated vessel, and one example of a

large vessel with a flat bottom, thinner than the vessel

walls. There is one grater plate (rallador), but the grooves

are not very deep, and it does not appear to be a function-

al manioc grater.

Surface treatments include polishing, brushing, inci-

sion' and impressions. Impressions derive from woven bas-ketry and reed mats. Some of the ceramics are painted or

slipped. The painted examples are either brown on light

brown or black on gray. In some cases the paint seems to

have been applied after firing. Painted designs are visible

on only two sherds. One fragment has a design made up of

repeated thin lines.

Analysis

There is a clear pattern of ring ditches along the Yacuma

and Rapulo rivers that share common characteristics and

Jour nal ofFieldArcha eologyjVol. 33) 2008 421

I_II lill.1A200 meters y

are associated with ceramic scatters. Ring ditches on these

two rivers are 1-12 ha in area, rougWy circular, generallyshallow (1 m), and 3-5 m wide. The ground surface with-

in the ditch is always higher than the surrounding land.

The ditches are located in forests on high ground, and

without exception, are associated with ceramics that are al-

ways within the circle and occasionally outside. All ring

ditches are associated with a source of water, such as a

creek, swamp, or river. Finally, they are widely distributed

both north and south of the Yacuma and Rapulo rivers.

Differences between the four examples are significant

(TABLE 2). San Francisco and Estancita are smaller (1-2

ha), and San Pablo and Zapuna are larger (10and 12 ha).

The two smaller ring ditches are located along the Yacumato the north, and the larger ring ditches are located along

the Rapulo to the south. The ditches at Estancita and Za-

puna are less defined, Zapuna much less so, while those at

San Pablo and San Francisco form complete circles.

Agricultural earthworks along the Yacuma are more ho-

mogeneous in form. Large raised fields are characteristic of

the Iruyafiez River basin to the north, and appear to be the

only type of agricultural earthwork along the Yacuma.

Yacuma raised fields are indistinguishable from those

found along the Iruyafiez. Were raised fields the only ar-


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pulo rivers are similar to earthworks in the Apere area,

where there are several different kinds of earthworks. The

clearest examples of ring ditches with a well-defined form,

however, are found near the modern town of Baures in

eastern Mojos. It is difficult to interpret Yacuma ring ditch-

es as defensive works, because their depth and breadth do

not form an effective barrier. It is possible that palisades

were con1bined with the ditches to lnake a n1uch more ef-

fective barrier, but as yet there is no direct archaeological

evidence of palisades. Ring ditches may also represent

"borrow pits" from which mound fill was tal(en. The earth

tal(en fron1 the ring ditch would only be a sn1all fraction of

the volume of a n10und that covered the entire area within

the ring. Nevertheless, it is likely that the soil from the

ditch became a part of the interior n1ound. Assuming that

movements of massive amounts of earth over long dis-

tances are unlikely, we can calculate the volun1e of earth

within the ring that can be attributed to accretional growth

(similar to the growth of a tell) and the volun1e that can be

attributed to the excavation of the ditch. At San Francisco,

for example, the earth moved froln excavating the ditch is

less than 100/0 of the volume of the mound inside the ditch.

Coincidentally, the earth moved to make the ditch was

roughly equivalent to one large raised field of average size

(based on the ten measured fields nearby).

Ditches necessarily had hydraulic functions, draining,

conserving, and perhaps n10ving water. In the seasonally

flooded savanna, the construction of any earthwork

changes water flows. The ring ditch at San Pablo is an ex-

ample of a simple earthen construction that could have had

an outsized effect on the surrounding environlnent and the

lives of the people who inhabited it. Because it connects a

flat, low-lying savanna with a seasonally flooding river, it

organized seasonal water-flow across the landscape. Along

with the water travel fish, animals, birds, and other re-

sources, all of which may have been in1portant to the

n1al(erS of the ring ditch. The high ground inside ring

ditches is a refuge for terrestrial fauna, a fact enthusiasti-

cally noted by local hunters. If in fact the interior of the

ring was inhabited, then those people would have placed

themselves at the juncture of a large river and a large area

of arable river back slope. At San Pablo, the area of back

slope affected by this drainage was at least 7 sq kn1.

All ring ditches have good access to year-round water

sources, although some have easier access than others. This

drainage does not seem to have been related to agriculture,

however, since the open space drained by the ring ditches

is usually mounded and always has ceramic scatters. Large

raised fields, obvious agricultural features, are also directly

associated with three of the rings. It is possible that ring

ditches were used to impound or store water, close to tl1e

422 Pr e-Columbian Ring Ditches along the Yacuma and Rapulo Rivers) Beni) Bolivia/Walker

End

Side

oI

5I

Figure 8. Fragment of a ceramic grinder (moleador), from the surface

of San Pablo Island.

chaeological evidence, the Yacun1a and Rapulo would be

placed in tl1e same category with the Iruyaiiez. To date,

there is no evidence of earthworks other than large raised

fields and ring ditches.

The ceramics of the YaCUlnaand Rapulo share charac-

teristics with both Iruyaiiez ceramics to the north and with

Apere ceramics to the south. To the south, grater plates and

grinders are common along the Apere, but virtually un-

known along the Iruyaiiez (Wall(er 2004). In our sInall

sample, one grater plate and one grinder were recovered.

Impressed ceramics are comn1on in all three regions. Flow-

ering rim bowls with painted designs on both sides of tl1e

rim and sponge temper are common along the Iruyaiiez,

but were not found along the Yacuma (Wall(er 2004).

Thus, according to this ceran1ic evidence, Yacuma potters

may have had more in common with those of the Apere

than the Iruyaiiez. At this time, chronological control is in-

sufficient to mal(e any definite statements about a ceramic

sequence.

Interpreta tion

The ring ditches and mounds along the Yacuma and Ra-


11/15

Table 2. Comparison of attributes of ring ditches.

Journal of Field ArchaeologyjVol. 33) 2008 423

Island area Ring ditch Height of

(ha) area (ha) Form mound (m)

San Francisco 2.7 1.06 Complete 1-2Estancita 30.3 2.24 Incomplete 2-3San Pablo 15.6 11.3 Complete 3-4

Zapuna 27.9-35.6 7-11 Isolated Pits 3-4

habitations within the ring. The hydraulic functions of the

ring ditches were thus quite significant.

Ring ditches also seem to have divided and organized

space. Activities that took place inside the ring resulted in

the deposition of broken pottery, while activities that took

place outside the ring did not. However else pre-

Columbian Mojenos used their ring ditches, they perma-

nently marked a line between the interior and exterior. Thiscould have generated and regenerated a sense of history

and place, similar to the one reflected in the IZuikurUmyth

in which a mythical ancestor is credited with digging cir-

cular ditches in all the good places to live (Villas Boas and

Villas Boas 1970: 163-165; Heckenberger 2005: 113).

Creating a ring ditch and defining a cultural space clear-

ly marks a group of people, malcing it easy to distinguish

insiders from outsiders. Just as raised fields define agricul-

tural places in the savanna (itself a built environment), ring

ditches create places that organize groups of people. Both

lcinds of definitions are used to manage agricultural sys-

tems (Ostrom 1990). It remains unresolved whether thispattern was associated with some lcind of permanent, cen-

tralized power that created and maintained that system

(Erickson 2006b).

Ethnohistorical Evidence

Based on historical and ethnographic evidence, the

Yacuma basin might be considered an empty space between

large raised field farmers to the north and causeway-build-

ing raised field farmers to the south. The evidence present-

ed here instead suggests an agricultural system similar to

that of the Iruyafiez basin to the north and a settlement

pattern resembling the eastern ring ditches. These earth-works extend the range of this pattern west across the

Mamore. It is likely that any regional pattern of earthworks

of different types in discrete zones across Mojos is only the

most recent (and therefore clearest) layer in a palimpsest of

earthworks. Ongoing survey, reconnaissance, and mapping

shows that there are a variety of earthworks within each of

these zones, and that there are few blank spaces between

them.

If they do circumscribe settlements, ring ditches along

the Yacuma represent towns larger than those described in

the ethnographic record for the contact period. The popu-

lation recorded by the Jesuits in the 17th century, and by

other observers in the 18th and 19th centuries, was prob-

ably much less than that of the 15th century. Before con-

tact with Old World diseases, the population of Mojos is

estimated to have been much higher (Denevan 1992). The

evidence of occupation from the Yacuma basin, although it

is fragmentary, supports higher population estimates.A brief summary of ethnohistorical evidence is necessary

to evaluate how ring ditches are used to understand

Arawalchistories. The ethnohistorical record for 16th cen-

tury Mojos has been admirably summarized (Block 1994;

Denevan 1966). As described by early sources, each major

group (what Denevan called the Savanna Tribes: Mojo,

Baure, Cayuvava, Canichana, Itonama, and Movima) has a

different constellation of material and institutional traits,

although they have many in common (FIG. 9). Denevan

notes that the Mojo and Baure have been classified as

"chiefdoms:' and that the Cayuvava might also be so

named.The Arawalc spealcing Mojo seem to have had villages

that were autonomous, although causeways connecting

villages suggest larger organizations. Although individual

villages had hereditary rulers with significant status,

Denevan concludes, "the evidence in the early sources is

not sufficient to indicate a situation significantly different

from a number of other tribes in the Amazon Basin"

(1966: 46). The Mojo were well known for their trade

contacts, ranging from Santa Cruz in the southeast to be-

yond the Beni River in the west.

The Baure also spealcan Arawalc language, and are the

easternmost of Denevan's groups. Their villages were sur-rounded by palisades and ditches and connected by cause-

ways. In other respects they are closely comparable to the

Mojo. Both groups were the focus of Jesuit attempts at

conversion throughout the 17th and 18th century.

The Cayuvava, who spoke an unclassified language

(now regarded by the Summer Institute of Linguistics as

extinct), were described in a letter by one Jesuit missionary

in a matter-of-fact way as having villages averaging 1800

inhabitants, seven of which were ruled by a single chief,

and a formal religious structure (Gordon 2005; Denevan


12/15

424 Pr e-Columbian Ring Ditches along the Yacuma and Rapulo Rivers) Beni) BoliviafWalker

Figure 9. Map of the Llanos de Mojos showing the distribution of several language groups (modified

from Denevan 1966, figure 3), the location of previously docwnented ring ditches, and the current sUldy

area.

1966: 350; Walker 2004: 26-27). This group and this

letter play an important part in Steward and Faron's origi-

nal description of savanna chiefdoms (1959: 252-261).

Block notes that this early reference is not supported by lat-

er historical accounts (Block1994: 18). Heckenberger de-

scribes the use of "chiefdom" here as the beginning of an-

thropological discussions of that term (Heckenberger

2005: 320).

The Canichana were a more centrally located, smaller

group that lived in small villages with palisades and moats,


13/15

and were described as fearsome cannibals. Denevan finds

no evidence for social stratification (1966: 53). The Itona-

ma, located between the Canichana and the Baure, are de-

scribed as uncivilized, naleed, and living in small villages.

Denevan suggests that they may have borrowed many

traits from the Mojo and Baure. Finally, the Movima oc-

cupied a large area west of the Mamore and were not held

in high repute by early authors; the best being said of them

is that they were numerous and covered a large territory.

Denevan notes that the "greatest concentration of cause-

ways and drained fields in the Beni" is to be found in this

area, an assessment that is still correct (1966: 52). He finds

it unlikely that the Movima were responsible for con-

structing earthworks, although he points out that they

might have changed considerably by the time they were

visited by the Jesuits.

Conclusions

If the ring ditch pattern is relatively clear, its interpreta-

tion is not. In recent discussions, Mojos earthworks are

taleen as evidence of an archaeological phenomenon relat-

ed to Arawalespeakers (Heckenberger 2005, 2006; Horn-

borg 2005). Ring ditches along the Yacuma River greatly

extend the known range of ring ditches in Mojos, and com-

bine with the spatial distribution of other kinds of archae-

ological evidence to suggest that Mojos was not dominat-

ed by any single language group. Ring ditches were ele-

ments in a regional landscape of different languages, in-

tensive economies, and political structures. Both Horn-borg and Heckenberger appear to see the archaeological

record in Mojos as a record of Arawak speakers:

The Southern Periphery [which includes Mojos] has asmuch to do with history as geography, and, although thesocial body is diverse, the skeleton, or deep cultural struc-ture, across much of the area is largely Arawal, in ori-gin. (Heckenberger 2005: 59)

The ridged fields in the Llanos de Mojos were probablyconstructed by the Arawak-spealcing Mojo... (Hornborg2005: 604)

In Heckenberger's account of Amazonian "deep histo-ry;' Arawalespealeersbuilt ring ditches in parts of Southern

Amazonia and across South America. Heckenberger ar-

gues forcefully that Amazonian peoples are not merely cre-

ators or creations of their environment. Their dynamic po-

litical systems have histories, initially oral and now also

written. Since Arawalespealeersaround the New World are

associated with intensive agriculture, earthen construc-

tions, and centralized political authority, the Arawalespeale-

ers in Mojos (the Mojo and Baure, principally) are held re-

sponsible for the creation of all earthworks and the devel-

Jour nal ofFieldArcha eologyjVol. 33)2008 425

opment of political centralization. Thus, the Mojo and

Baure add to the number of South American cases in which

this complex of Arawale traits is found. Heckenberger

seems to imply that these traits form a coherent package;

that Arawale spealeers built ditched villages, had intensive

agriculture, and were politically centralized, and that evi-

dence of these traits is found in scattered places as a result

of Arawak migration.

In Hornborg's understanding of ''Amazonian prehisto-

ry;' the builders of ring ditches are also assumed to be

Arawale, but with a significant difference. Hornborg em-

phasizes the language, rather than the spealeers, and the

package of'~awalc" traits (including ring ditches) adhere

not to the speakers, but to the language. Hornborg argues

that pre-Columbian peoples created world-systems of in-

teraction and trade before their contact with the Old World

(see also Lathrap 1973). The distribution of Arawak istherefore evidence for a continent-spanning system of

long-distance trade and the movement of ideas and goods

across South America. This model may be more appropri-

ate to Mojos, where only two of six major language groups

have been classified. Mojeiios probably included raised

field farmers, foresters, gatherers, and hunters; spealeersof

Mojo, Movima, Cayuvava, and Baure; dwellers in settle-

ments of 2000 and wandering groups of 20. Any of these

categories may have overlapped.

Nevertheless, not all ring ditches are spatially associated

with ethnohistorical distributions of Arawak speakers.

They are spread over an area of at least 20,000 sq km, andsome are associated with at least two different kinds of

raised fields. The re-discovery of ring ditches in areas asso-

ciated with non-Arawale spealeers in Mojos suggests that

earthworks are not necessarily connected to Arawalespeale-

ers. Ring ditches and the discrete agricultural systems sur-

rounding them were not always spatially linleed to Arawale

languages.

There is no doubt that Arawak speakers are present in

Mojos today, and that they were present at contact and in

pre-Columbian times. I would argue that Denevan's sum-

mary is still relevant: there were six principal language

groups present in Mojos at the time of contact, whosecombined territories are roughly coterminous with the sa-

vanna. Of these six, two were Arawak (Mojo and Baure)

and four were isolated languages (Movima, Cayuvava,

Itonama, and Canichana), one of which was possibly Tu-

canoan (Canichana). At the time of Denevan's work, earth-

works had been documented throughout areas inhabited

by the Mojo, Baure, Movima, and Cayuvava.

The presence of ring ditches in central Mojos, in the

midst of an area associated with non-Arawale spealeers(the

Movima) maleesproblematic any exclusive historical con-


14/15

426 Pre-Columbian Ring Ditches along the Yacuma and Rapulo Riversy Beniy BoliviafWalker

nection between ring ditches and Arawak speakers. In

some cases, it might seem possible to draw a direct geo-

graphical connection between types of earthworks and lan-

guage groups. For example, large raised fields (found along

the Iruyafiez, in Cayuvava territory) could be associated

with the Cayuvava, while ring ditches, found along the

tributaries of the Itenez, in Baure territory, could be asso-

ciated with the Arawak speaking Baure. Along the Yacuma

both kinds of earthworks are present in an area that is his-

torically associated with a third group, however, and this

suggests a more complex interaction. Almost 200 years

elapsed between the Conquest and the arrival of the Jesuits

in Mojos, and it is likely that there were considerable

movements of ideas and of people during that interval.

A direct geographical connection between Arawak

speakers and ring ditches would explain the Baures ring

ditches, but not those from the Yacuma. If there is no di-rect geographical connection between Arawak speakers and

earthworks, then it is not clear why Arawak spealcers

should be granted the exclusive status of raised field

builders, when there are four other populous savanna

groups nearby, and ring ditches also occur in the center of

the area occupied by the Movima.

This argument is something of a straw man, and I do

not suggest that either Heckenberger or Hornborg draws

a simple connection between a single type of material evi-

dence and a language group. I do maintain that both pub-

lished interpretations overemphasize the role of Arawak

speakers in Mojos and downplay the multiethnic history ofthe region. Moving forward, it is possible to examine ring

ditches and landscape features as part of a palimpsest that

includes the entire Mojos savanna. We can use GIS and

spatial analysis to think about the landscape in this way,

and it may lead to new insight about pre-Columbian land-

scapes in Mojos and throughout South America.

Acknowledgments

The author would like to thank the many people and in-

stitutions in Bolivia and the United States who made this

research possible. In La Paz, the Instituto N acional de Ar-

queologia de Bolivia and its director Javier Escalante weregracious and helpful. Freddy Arce assisted with adminis-

trative matters. In Trinidad, thanks go to Oscar Saavedra,

Arnaldo Lijeron, Rodolfo Pinto Parada, Ricardo Bottega,

Celia and Teresa Perez Chavez, the Universidad Autonoma

del Beni, the Prefecture of the Beni, the Museo Etnoar-

queologico "IZenneth Lee;' and the Fundacion IZenneth

Lee. In Santa Ana, heartfelt thanks to Jaime and Georgina

Bocchietti, the Museo Regional de Arqueologia Yacuma,

the Alcalde and the Sub-Prefecto, and Senores YamilN acif,

Ascarrauz, y N aci Without the goodwill and cooperation

of all of these friends and institutions, this research would

not have been possible.

In the United States, this research was funded by the

University of Central Florida's College of Sciences. Help-

ful comments on the manuscript were provided by Greg

Borgstede, Charles Golden, Chris Dayton, Richard Burg-

er, and one anonymous reviewer.

John H. Walker (ph.D. 1999y University of Pennsylvania) is

an Assistant Professor at the University of Central Florida

and an archaeologist working in the Bolivian Amazon. He

studies the link between social O1:ganizationand spatial pat-

terns by integrating survey and excavation into GIS using

GPS a nd other technologies. He has worked in eastern Bolivia

since1992y and ispart of the Archaeological GIS Project of

the Beni) a long-term project meant to systematize survey andexcavation acrossthe Beni a nd integrate it into a database ac-

cessibleto Bolivian and international scholars.Mailing ad-

dress: Howard Phillips Hall 309) 4000 Central Florida

Blvd.) Orlando) FL 32816-1361. E-mail address: jzwalk-

[email protected]

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