Geoglyphs in the Andean Central Coast: combining digital and traditional survey techniques

Abstract

This Andean coast research has identified 113-plus geoglyphs spanning the Formative (1800–100 BC) to the Inka period (AD 1470–1532). The project combined digital technology and Remotely Piloted Airborne Systems to locate the sites. The authors also documented examples of ceramics and intricate road systems and suggest that the finds represent meticulously ritualised landscapes.

Introduction

The middle Chillón valley, situated on the Andean central coast (Figure 1), has been the subject of extensive scholarly investigation for nearly half a century (Dillehay 1976; Silva 1996); however, the deep ravines that traverse into the valley remain relatively unexplored. Research undertaken from 2019–2024 has revealed geoglyphs dating from the Formative (1800–100 BC) to the Inka period (AD 1470–1532). Documenting these large-scale (minimum of 4m in length) examples of land art presents methodological challenges, but digital technology and the use of Remotely Piloted Airborne Systems (RPAS) prove effective solutions.

Figure 1. Middle Chillón valley and the areas surveyed (figure by authors).

Through the use of publicly accessible satellite images (Google Earth), photogrammetric drone surveys and systematic field surveys, we have successfully recorded 113 previously undocumented geoglyphs representing a varied typology.

Geoglyphs in southern Peru are usually found in the Andean region, particularly in the Nasca and Palpa areas (Lambers 2006; Sakai et al. 2014); they are also present on the north coast (Alva & de Alva 1982; Pozorski et al. 1991; Shady et al. 2003), but there is limited information about the central coast. Our research challenges this geographic confinement and the findings indicate a high concentration of geoglyphs on the central Peruvian coast—most notably in the Chillón river valley, focus of our research. Information pertaining to the central coast has been limited to the Rimac river valley (Rosello 1997; Abanto 2009) and a small number of sites in the Chillón river valley: San Diego, Torre Blanca and Macas (Rodríguez 1999; Palacios 2017).

Comprehensive recording in the middle Chillón valley

Along the Chillón river, 113 previously unreported geoglyphs have been documented (Figure 2). Linked with examples of ceramics, intricate road systems and other evidence, these findings suggest meticulously ritualised landscapes. Formative and Wari geoglyphs were situated near ceremonial and administrative centres, whereas those associated with regional states and Inka sites were in proximity to crossroads and formal pathways. The investigation primarily focused on identifying geoglyphs and their associated elements by analysing spatial, morphological and visual aspects through a multiscale remote sensing methodology. Similar research methodologies have been successfully applied in other regions (e.g. Lasaponara & Masini 2012; Lambers 2020), which influenced our chosen approach.

Figure 2. Huarabi Geoglyphs, Formative Period: a) geoglyph 1; b) geoglyph 2. Images taken using RPAS (figure by authors).

Furthermore, this research methodology yields georeferenced maps that are crucial for on-site investigations. The digital maps can be seamlessly integrated into GPS and mobile devices (Chen et al. 2017; Abate & Lasaponara 2019), offering a practical advantage when undertaking ground survey such as real-time navigation and enhanced accuracy. This information is particularly valuable for geoglyphs situated in challenging or remote areas or those that have undergone alterations due to reasons such as urban development.

The identification of geoglyphs began with examining Google Earth satellite images. Initially, we noted terrain irregularities suggesting ‘potential’ geoglyphs. We then used RPAS—Mavic 1 drones and PHANTOM 4 PRO—for verification. Images captured at 30–70m had resolutions of 10mm/pixel (Mavic 1) and 30mm/pixel (PHANTOM 4 PRO). These images were processed with Agisoft Metashape software to generate 3D orthophotos.

The final phase involved a comprehensive field survey for validation, correction and documentation of the material culture associated with the identified geoglyphs. This integrated approach, including satellite imagery analysis, RPAS utilisation and field surveys, ensured a robust and multifaceted methodology for geoglyph identification and analysis.

Results

This methodology facilitated the documentation of more than 113 geoglyphs across 19 archaeological sites (see Table S1 in online supplementary materials). The ceramics found at each site were not employed as an exact chronological indicator. Instead, their presence allows for cautious inferences to be drawn regarding the relative chronology of the geoglyphs and, possibly, their final use. However, initial analysis of the ceramics identified one site from the Formative period (1800–100 BC), four from the Regional Development period (100 BC–AD 900), one from the Wari period (AD 900–1270), and 16 from the Regional States and Inka periods (AD 1270–1532) (Figures 3 & 4). Subsequent studies should consider other factors for refining chronologies, such as cultural reuse, post-depositional and taphonomic events that may have influenced the distribution of these ceramics.

Figure 3. a & b) Macas, Wari period; c & d) Zapan, regional states and Inka periods. Images taken using RPAS (figure by authors).

Figure 4. a) Gangay, regional states and Wari periods; b) Algodonales, regional states and Wari periods. Images taken using RPAS (figure by authors).

Nonetheless, it is important to note that geoglyphs tentatively linked with Formative ceramics are situated near U-shaped buildings, such as at Chocas and Pucara, which were pervasive religious/ceremonial structures during the Formative period (Williams 1980). The geoglyph from the Wari period is most likely affiliated with the Wari site of Macas, while those from the Regional State and Inka periods are aligned with both primary and subordinate crossroads (Figure 5).

Figure 5. Pre-Hispanic road system associated with Huachipuquio. Image taken using RPAS (figure by authors).

Geoglyphs served as a profound cultural expression of the communities residing in the middle valley of the Chillón river. These manifestations of cultural lifeways intricately incorporate vast expanses of wilderness and desert into their belief system. Through deliberate and meticulous landscape modifications, these geoglyphs were strategically positioned to be visited by multiple communities, thereby fostering a cohesive integration of different polities (Schwimer et al. 2024).

Owing to their geographic isolation, the geoglyphs remain unaffected by modern alterations. The recorded paths seem to connect the valley inhabitants solely to the geoglyphs, given the absence of other pre-Hispanic constructions nearby. Thus, the geoglyphs and paths likely formed a highly significant space used by the middle-valley inhabitants of the Chillón river for various rituals.

In Andean societies, religion intertwines with economic, political, corporate and domestic activities, a concept known as Embedded Religiousness (Mesia-Montenegro & Sanchez-Borjas 2023). Sacralising landscapes through religious markers such as geoglyphs is central to this. These markers hold religious and political significance, serving as cultural boundaries or convergence points, deeply embedding religion into daily life.

Conclusions

Geoglyphs have played a pivotal role in shaping the cultural and physical landscape of central Andes coast societies, with the middle Chillón valley serving as a poignant testament to the profound significance and coexistence of geoglyphs alongside ceremonial spaces, such as Formative U-shaped buildings or Wari sites such as Macas, or intricate road systems. The archaeological evidence suggests that the practice of constructing geoglyphs in the middle valley of the Chillón river might have persisted for more than 3000 years.

Unfortunately, the ongoing rapid and disorganised urban development this century in the region poses a significant threat to these previously unreported geoglyphs. Preserving this invaluable cultural heritage necessitates strict adherence to established heritage-preservation regulations. The studied area not only boasts a rich array of geoglyphs but also encompasses a wealth of surface material culture, including ceramics and pre-Hispanic roads, some potentially linked to the Inka Road system (e.g. Hyslop 1984). Moreover, the potential existence of similar sites in other valley segments cannot be dismissed.

To address these potential discoveries, it is crucial to broaden the scope of research within the valley. This involves exploring intra-valley communications via ravines, utilising a combination of RPAS and traditional survey techniques. Such an expanded research approach promises to contribute to a rounded understanding of the region's cultural heritage and will play a vital role in formulating effective preservation strategies.