Multidisciplinary approach for archeological survey:exploring GPS method in landscape archeology studies**

Alessandro Capra a, Stefano Gandolfi b, Laura Laurencich c, Francesco Mancini b,Alberto Minelli d, Carolina Orsini c,*, Aurelio Rodríguez e

aFacoltà di Ingegneria di Taranto, Politecnico di Bari, V.le del Turismo 8, 74100 Taranto, ItalybDipartimento di Ingegneria delle Strutture, dei Trasporti, delle Acque, del Rilevamento e del Territorio, Università degli studi di Bologna,

Viale Risorgimento 2, 40100 Bologna, ItalycDipartimento di Paleografia e Medievistica, Università degli studi di Bologna, P.zza San Giovanni in Monte 2, 40100 Bologna, Italy

dDipartimento di Biotecnologie agrarie ed ambientali, Università degli studi di Ancona, via Brecce Bianche, 60100 Monte Dago, Ancona, ItalyeInstituto Nacional de Cultura, Av. Javier Prado Este 2465, San Borja, Lima, Peru

Abstract

Started in 1996, the Chacas Valley Project is coordinated by Laura Laurencich Minelli and aims to study the social–cultural organizationof space in the Chacas Region (Ancash-Perú) during the Early Intermediate Period (III–VII century A.D.). For an anthropologicalinterpretation of ancient urbanized territory, a multidisciplinary approach focused on gathering both archeological data and topographicalinformation is necessary. The kinematic GPS method has been applied in order to reach the needed accuracy in representing the geometricproperties of the objects, to preserve the geometric properties between the structures and to document the relations with the groundmorphological aspects. © 2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved.

Keywords:Archeological survey; Kinematic GPS; Peru; Pre-Columbian settlement patterns; Recuay

1. Research aims

The Chacas Valley Project (C.V.P.) began in 1996 withthe aim of studying the settlement patterns of pre-Columbian civilizations of Chacas Region (Ancash-Perú,see Fig. 1) during the Early Intermediate Period (III–VIIcentury A.D.). For the study of ancient urbanization sys-tems, it is essential to integrate archeological, topographicand geodetic applications, which can helpfully provide allthe geographic information essential for the archeologicalinterpretation of settlement systems. This is why a closelyrelated collaboration among researchers in history andarcheology and researchers in surveying, geodesy and

photogrammetry was started, not only during fieldwork butalso during post-campaign data analysis and processing.

The research involved an archeological mapping ofChacas Valley, and has been successively focused on thecitadels of Huacramarca and Riway.

These citadels are very important because they representone of the ancient examples of urban settlements built athigh altitude (over 4000 m above sea level). Furthermore,Huacramarca and Riway are unknown expressions of Rec-uay culture, a civilization mainly studied from ceramics butnot from urban settlements. Due to the archeological impor-tance of these two citadels, an accurate topographic surveywas needed.

The surveying technique allows the positioning of ar-cheological sites in local and national cartographic systems,and for this purpose, it was essential to set correlationbetween different settlements using both spatial and tempo-ral analysis.

In effect, the first goal was to obtain the correct position-ing of the archeological sites on the Peruvian referencesystem. This was the starting point to have a complete andhomogeneous idea of the valley’s settlements. The area in

* Corresponding author.E-mail address:orsinic@cib.unibo.it (C. Orsini).** F. Mancini and C. Orsini worked on data and figures and edited

the present paper. A. Capra and L. Laurencich coordinated the fieldworkand collaborated in writing this paper, and R. Rodriguez codirectedthe fieldwork during the 2001 campaign, while G. Gandolfi worked on fielddata collection and wrote Section 3. A. Minelli worked on field datacollection.

Journal of Cultural Heritage 3 (2002) 93–99

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which we were interested is covered by Peruvian cartogra-phy at a scale of 1:100 000, a relatively small one that is notsufficient for detailed positioning. The monographs of a fewtrigonometric vertices have been recovered from the avail-able geodetic system, but we were unable to find them on

the ground. So it was necessary to create new referencestations with an approximated connection to Peruvian car-tography. The long distances involved and the irregularmorphology of this area made the GPS topographic surveynecessary for positioning archeological sites and for provid-

Fig. 1. Map of Chacas Valley and points adopted as a reference for the archeological survey. (1) Stations placed in Huacramarca and Huallin; (2) station SanLuis; (3) station placed in Riway; (4) station placed in Piscobamba.

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ing a detailed description of structure distribution in archeo-logical sites. Furthermore, the GPS method was essential inorder to define the shape and geometry of different struc-tures in relation to the area’s morphology. In fact, thismethod was useful not only to describe single structuregeometry but also to register the position of differentelements and to relate them with the ground surface trend.The last aim requires a survey based on GPS in kinematicmode.

During fieldwork, archeologists made an exhaustiverecord of all data directly associated with the structures, likeinformation on the morphology of the land, the type ofvisible landscape and landmarks (the position of Huacrama-rca and Riway being in strategic places, obviously thisfactor was of paramount importance), on the eventualvicinity of rivers, water mirror, etc., and other informationrelated to the “visual logons”, so important in pre-Columbian times (e.g. the sight of a mountain, a ceremonialcenter, etc.), has also been recorded.

In past campaigns, total stations and classical topo-graphic instruments were used, but only for preliminaryinvestigations, while, successively, GPS methods were ap-plied in order to reach the needed productivity and accuracy.

As a final result, we computed the digital elevation modelof the areas from the collection of a lot of surveyedkinematic GPS points distributed homogeneously on theground and automatically sampled every 5 s. The simulta-neous view of archeological settlements and morphologydescribes the urbanization of the sites in a very accurate anduseful way for data interpretation.

In the following text, we present a description of thehistorical and archeological context of Chacas Valley, areport of the survey techniques and, overall, some newarcheological results derived from accurate and extensivesurvey application.

2. Archeology, geography and economyof Chacas Valley

The Chacas valley is of glacial origin, and it is placed inthe heart of the Andes, on the eastern side of CordilleraBlanca, in the so-called Callejón de Conchucos. It occupiesan area that extends in the northerly direction betweenlongitudes 77°20' W and 77°15' W and latitude 9°4' Sapproximately.

The valley takes its name from the principal village,founded in 1572–1573 by a group of Spaniards. TheConquistadors probably established their settlement over animportant pre-Hispanic center, as we can infer from thearcheological remains in the northern portion of the village,known as Pirushtu, a monumental site composed of twomounds that surround a central rectangular plaza orientedfrom east to west. It is possible that, nowadays as well as inthe past, Chacas (3359 m above sea level) was an aggrega-tion center because of its strategic location on the roads that

linked the coast of the Pacific Ocean and the Amazonianrainforest.

The Spanish were attracted to the valley by the possibil-ity of exploiting mines of copper and silver. In ancienttimes, some gold was collected from the bed of the rivers aswell. Today, the vast majority of mines have been aban-doned, and the local economy is based on stock raisingEuropean livestock, together with some cultivation andtrade. In the pre-Columbian age, the extraction of metalsand the stock raising of llamas seem to have been the baseof the economy.

The Chacas valley offers a great abundance of archeo-logical remains, many of which have common characteris-tics: these places are known to the local population, andsome of them appear on local, but not on geo-referenced,maps.

However, the isolation of the valley and the intenseactivity in this zone of the guerrilla movement “SenderoLuminoso” until the early years of the 1990s have notallowed scientific surveying of the pre-Hispanic sites.

Nowadays, archeological surveys in the northern part ofChacas Valley are conducted by Alexander Herrera-Wassilowsky [1]; otherwise, current research on the central

and southern part of the valley is led by Laura Laurencich-Minelli (director of C.V.P.) and (in 2000) by Aurelio

Rodríguez Rodríguez. Recently, the pottery collection of theMunicipality of Chacas has been extensively studied byLaura Laurencich Minelli [2], Carolina Orsini [3] andSteven Wegner [4] as well.

The archeological zones identified by the C.V.P. re-searchers until today are located both in the lower parts ofthe valley (especially the ceremonial centers), and in theelevated zones (high plateaus called puna or jalca in thelocal Quechua language), ranging from 4100 to 4800 mabove sea level.

In the jalca, the characteristic vegetation is ichu, com-posed of varieties of several species: calamagrostis, stipaand festuca, Andean xerophytic plants. The jalca is veryfavorable for the stock raising, but not for harvesting;therefore, it is natural that, in pre-Columbian times, thejalca was urbanized by shepherd’s communities. Two ofthese shepherd’s sites, Riway and Huacramarca, were inves-tigated in depth in this project.

Inspections carried out from 1996 to 1998 allowed us toindividuate various archeological remains, and to sketchmaps of Riway and Huacramarca. Detailed mapping andceramic recollection was brought out in Riway during the1999 campaign, and in Huacramarca during the 2000campaign.

Since the first inspections (from 1996 to 1998), archeo-logical surveys allowed us to establish that the largestportion of the remains visible today dates back to the EarlyIntermediate Period. However, we know that the valley wasinhabited from almost 200 B.C.: some monoliths stored inthe school of Chacas show Chavinoid-style features, that isthe influence of this ancient culture which flourished be-

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tween 900 and 200 B.C. in the same region. The mostancient ceramics found in the zone (and today conserved inthe archeological collection of Chacas Municipality) aresome Huarás-style blanco sobre rojo pottery (200B.C.–200 A.D.) [4]. However, no Huarás settlements havebeen found in the Chacas valley until now.

3. The GPS reference system

In general, a geodetic GPS survey that refers only to alocal reference frame can only show relative informationsuch as size and shape of the surveyed objects. Orientation,cartographic superimposition, geographic information sys-tem realization and other studies can be performed onlyfrom a correct location of the survey in a global referenceframe and in a well-defined cartographic reference system.

In a stand-alone configuration, the GPS system furnishescoordinates in both geocentric and global reference frameswith 10–50 m accuracy, not feasible for the applicationsunder discussion.

Usually, the correct approach consists of a survey (GPSdata collecting) over some official cartographic vertices ofthe national network (where cartographic coordinates areknown), using also the closest GPS reference stationsincluded in the ITRF (International Terrestrial ReferenceFrame) computation. Several transformation parametersfrom these sets of coordinates transform all the surveyedpoints on the desired system, taking also into account thecartographic local distortion due to several problems mainlyrelated to the older methodology utilized for measurementand data adjustment.

On the other hand, maps of the Peruvian Andes are poorin detail, and sometimes, they are not updated with infor-mation related to recent settlements, villages and topono-mastics. Prior to the topographic expedition, some mono-graphs of points of the National Peruvian Network wererecovered from the I.G.N. archives (Instituto GeográficoNacional del Perú), but unfortunately, once in the field, theexact locations could not be found. To cope with the lack ofa reference frame, a group of new GPS stations werecreated, and survey was conducted within the area includingthe sites of archeological survey. The coordinates of thestation located at Piscobamba, considered as the mainstation in the area, were derived by a very long single pointpositioning using a dual-frequency GPS receiver. The othercoordinates of the network have been consequently derived.

The transformation of the GPS coordinates in the localnational system can be obtained by the use of the low-accuracy parameter transformation based on the differentorientation and dimension of the ellipsoids used in datumdefinition.

Moreover, the official Peruvian cartography (1:100 000scale) does not require great accuracy, when the aims arebasically updating and representation over the same maps.This level of accuracy is also sufficient when cartography is

derived from aerial stereo-photographs, which is the casefor most Peruvian maps.

However, taking into account not only the global projectbut also the survey of several archeological sites in theChacas valley, the institution of a static network is useful tomake available a reliable set of coordinates. This networkconstitutes our reference frame for the local, kinematic andstatic survey of the archeological sites studied.

4. Kinematic GPS for archeological survey

The primary goal of the above-described archeologicalsurvey was the detection of all existing structures within theRecuay settlements using an efficient technique, consideringthe short time planned for fieldwork due to logistic con-strains. Differential kinematic GPS provides a very produc-tive and highly accurate (up to a few centimeters) method-ology when dual-frequency GPS receivers are employed inboth real time and data post-processing [6]. In each case, thesurveyed position representative of a given object waslinked to an alphanumerical attribute and determined withreference to the three-dimensional coordinates of the fixedstation. The station used as reference is typically a well-recognizable feature close to the area of interest andcarefully connected to those belonging to the referenceframe. The accuracy of the final GPS positions collected bythe rover receiver basically depends upon the distance tothis point. In many cases, it ranges from 1 cm, if very shortdistances are involved, to tens of centimeters when longervector baselines are calculated for positioning. Using thisconfiguration, the data collected by the reference stationsand the rover receivers allowed the connection of the fixedstations to the local GPS reference system and, at the sametime, the post-processing of the kinematic surveys using theOTF (on the fly) algorithm as solving strategy. OTF affordshigh accuracy because of its ability to solve the carrierphase integer ambiguity of signals belonging to a roverreceiver. Ambiguity resolution is the determination of fullcarrier cycles over two frequencies, and it is essential forhigh-precision positioning. As a final result, the GPS dataprocessing furnished the three-dimensional coordinates ofall the surveyed objects within the boundaries of the citadelsof Huacramarca and Riway, rigorously preserving all infor-mation about metric aspects (scale and distance) of thetagged points and structures in a well-defined referencesystem.

The final positions (several hundreds for each survey) areat first referred to the WGS84 datum in geographical formatand could be easily exported to a different datum andprojection like the Peruvian South America Provisional1956–UTM system. The last is the case.

During the same kinematic survey, many other pointcoordinates and single target positions were acquired, usingthe automatic sampling rate (5 s) and manually, for a betterdescription of the main morphological structures. Once back

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in the office, a digital terrain model (DTM) was generatedusing the large number of points acquired, adopting krigingas the scattered data interpolation method. The superimpo-sition of the DTM with a preview of citadel structuresprovides much useful information for the reconstruction ofthe archeological data and interpretation of the population’severyday life (see Fig. 2).

The virtual surface is a proper and coherent referenceplane for the final representation of Huacramarca and Riwaycitadels, thus rendering immediately the image of the truefield situation.

5. Huacramarca

Huacramarca (see map, Fig. 3) is located 4141 m abovesea level, on the homonymous mountain. On its westernside, the erosion of Potaca River has formed a valley with aquite narrow sedimentary plain, and on the eastern side,another deep valley has been formed by Garguanga River(Qarwanqa, “River of the Sacred Red Stone”). As for otherarcheological sites of the Chacas valley, no previous studiesexist, but the zone is well known to the local population, andit was described by Saúl Espinoza Milla [5] as an importantpre-Columbian citadel, characterized by chulpas1 and acircular three-level stone building apparently destroyed inthe recent years, which we were unable to locate.

Huacramarca has an extension of approximately50 000 m2; its shape is almost rectangular, and it is nearly200 m long and 250 m wide. Its main axis is orientedapproximately in the north–south direction. Its position,atop a precipice, from which three valleys and several riversare visible, seems ideal for the defense and control of a vastpart of the valley. The closest present-day village is Huallin(3525 m above sea level.). In the vicinity of Huallin, aceremonial center has been identified, called the Pirushtu ofHuallin. The Pirushtu of Huallin is visible from a sector ofthe citadel.

It is possible to reach Huacramarca by different ways, butin the past, the main access was probably from the Potacariver valley. Here, nowadays, it is still possible to see anancient road beginning in the external margin of a group ofagricultural terraces. Before the last climb to the citadel, asmall terrace accommodates some rough circular structures.The access to the citadel is defended by natural cliffs, and bywall structures where cliffs are low. A narrow path throughthese cliffs leads to an open space characterized by thepresence of a wall with a door (the “monumental” entranceto the citadel). Immediately over it, numerous structuresoccupy an enormous open space. Generally, constructionsare arranged in small square rooms adjacent to a nearlycircular open space, probably corrals for the llamas or anyAndean camelids.

According to the morphology of the structures andaccording to some ethnographic analogies, we can suggestthe use of these recints and divide the citadel into sectors.The sectors are individuated by a number, while thestructures inside each sector are individuated using a letter.The entrance sector (0a, 0b, 0c) does not accommodate anystructure, but here, above a natural fissure of a cliff, aseverely looted burial structure and some traces of burialofferings were found: the scattered remains of a humanadult and, beside, a finely worked bone artifact. The lowerpart of the citadel seems to have been the residential zone,occupied by the elite population (sectors 1, 2, 3, 4, 5, 6),while the upper part (sectors 7, 8, 9, 10, 11) is theceremonial one. The ceremonial zone has a complex mor-

1 Chulpa is a Quechua word, often used to describe monumental,square or circular burial buildings designed to store mummified bodies ofdead people, considered the ancestors of Andean ethnic groups.

Fig. 2. Superimposition of the Huacramarca archeological structures toDTM.

Fig. 3. Map of archeological site of Huacramarca.

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phology: it is formed by two elevated zones joined by adepression in the form of a square (sector 8), where an altarof non-local carved white granite (probably for sacrifices)was found.

In this sector, the activity of huaqueros (the local treasurehunters) and erosion was extremely destructive. The cer-emonial sectors (7, 8, 9, 10 and 11) are located on differentlevels in a stairway-like arrangement (see Fig. 1, sectors 8,9) that probably had ritual meaning. On the eastern side ofsector 10, two chulpas in a good state of preservation werefound. At the end of sector 9, high and sharp cliffs block theaccess to what seems to be one of the most sacred sectors(11). Here, two small chulpas, probably used to storemummified human bodies, were incredibly constructed onthe steepest side of the cliff. From the citadel, the tombs arevisible only from this sector: both are perfectly camouflagedin the mountain, but they can also be seen from the bottomof the Garguanga river valley, which, at this point, forms adeep gorge.

Finally, sector 13 (not included in the map) is located faraway from the citadel, in a northeast direction. Here, wefound some remains of a two-level funerary structureleaning on a cliff. It has been partially destroyed byhuaqueros. Inside the construction, called chulpa amarillafor the characteristic color of the yellow mortar that coversit, some human bones in a bad state of preservation werefound.

6. Riway

Riway (see map, Fig. 4) is located at an altitude of4012 m above sea level on the homonymous mountain, at aone-and-a-half-hour walk from the modern village ofSapchá. Mettere l’altezza.

The archeological site develops in an east–west direction.Its morphology, like that of Huacramarca, is characterizedby a double mound construction in the highest part of thecitadel. The highest part of the site occupies an area of5694 m2, and it is surrounded by enormous, well-constructed stone walls. The southern side of the mountainis limited by discontinuous walls, and it degrades into arather steep slope to a height of 3900 m above sea level,while in the north, the slope is gentler and there are nowalls, but some rather scattered architectural remains oc-cupy an area of about 15 000 m2.

The whole site has been divided into two areas, respec-tively, the higher part and the lower part.

As in the case of Huacramarca, according to the mor-phology of the structures, we have assumed a different usefor each part, and we have divided the citadel into sectors:

Sector 1: ancient defended access to the citadel consti-tuted by a narrow passage formed by two parallels walls andcontrolled by a tower-like structure.

Sectors 2–3: residential sector.Sectors 4–6: probable ceremonial sector.Sector 5: passage sector, with defensive walls. Some

square underground structures were probably used as ware-houses.

Sectors 7–9: ceremonial squares limited by walls. Here,an intense activity of clandestine digging and looting hasrevealed numerous subterranean burials.

Sector 10: probable ceremonial sector. It is limited by adouble ring of walls with inner rooms and other minorbuildings on the inside, probably the heart of a cult place,where two small stone-lined offering traps have been found.

Sector 11: burial zone. A mound-like elite burial buildingwith an inner chamber, limited by square stone walls andused for burial in ancient times, were found.

7. Conclusions

GPS survey applied to archeological research has sup-plied excellent results. The quality and productivity of theinformation obtained are very high. GPS allowed us toobtain quick geocoded data in a reference system created adhoc for our purposes with a high accuracy level of coordi-nate values (below 5 cm). Furthermore, data available canbe immediately transformed into thematic maps useful forintegration into a geographical information system (GIS)application.

The space relation between geographic and urbanizedlandscapes is the most important data achieved during thearcheological research with this methodology. DTM reliefhas brought to light the construction of the citadels onnatural mountains modeled in the higher parts by humanwork, in order to construct two mounds joined by a plaza.This particular morphology has been found also in otherRecuay settlements (like Queyash Alto, in the Callejón deHuaylas) and allows (together with ceramic data analysis) aFig. 4. Map of archeological site of Riway.

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relative dating of the citadels with a good margin ofcertainty. Another important information provided by theDTM survey was that the citadels were constructed abovesome well-structured terraces that were more and morereduced, and were less accessible when approaching the twomounds. In Riway, as in Huacramarca, the mound nearest tothe inhabited zone is the most accessible, while the other ismore isolated and seems to be closer to the burial zone. Infact, the Riway burial sectors (7, 8 and 9) are closest tosector 6, which is the highest mound and the farthest fromthe inhabited sectors. In Huacramarca, sector 10, whereburial chulpas were found, is very close to sectors 9 and 11,those that constitute a mound on two levels. The othermound of sector 7 is situated immediately above theinhabited zone. In both urbanization systems, it is clear thatthe highest zones had restricted access, and probably, themummies of the founding ancestors of the ethnic groupwere buried there. Finally, DTM brought to light tworestricted areas that probably had different meanings. As apreliminary result, we can argue that the more isolatedmound should be a sacred zone in connection with burialrites, while the mound close to the inhabited zone wasprobably a sacred zone devoted to public ceremonies.

Another observation found from DTM relief is that bothcitadels are constructed above 4000 m in isolated places andclose to rivers.

Future campaigns will allow the perfection of the appli-cation of GPS methodology in archeological survey, inorder to contribute in creating a standard for the applicationof this methodology to archeological research.

Future goals are: (i) to apply the obtained methodology toa large number of archeological sites with similar charac-teristics; (ii) to model the archeological survey proceduresto the new technology; (iii) to acquire more data useful fora three-dimensional metric reconstruction of the structures.

We also aim, during post-campaign data processing, toorganize information in the easiest way for archeologicalinterpretation and for transfer.

References

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[2] L. Laurencich, The Chacas Museum: the heart of Eco-Museum, in:L. Laurencich, S. Wegner (Eds.), El Museo de Chacas, EditoriRiuniti, Bologna, 2001, pp. 37–64.

[3] C. Orsini, Space symbols in the Recuay ceramic collection of themunicipality of Chacas, in: L. Laurencich, S. Wegner (Eds.), ElMuseo de Chacas, Editori Riuniti, Bologna, 2001, pp. 65–106.

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