U-shaped power: Infantas and the ritual-political nexus of Formative-period monumentality in the Chillón Valley, Perú

Abstract

Excavations at the Infantas complex in Chillón Valley, Perú, revealed a U-shaped monumental centre with a central mound, clay staircase and columned atrium. Aligned with structures from the Rímac and Lurín valleys, these complexes anchored ritual-political power, serving as hubs for ideological integration and territorial organisation in early Andean societies.

Introduction

The U-shaped architectural tradition, a hallmark of the Andean Formative period (2100–200 BC; Williams 1980), features monumental complexes consisting of central pyramidal mounds with two flanking arms enclosing large ceremonial plazas to create the characteristic ‘U’ shape. Concentrated in the Chillón, Rímac and Lurín valleys (Figure 1), these sites integrated religious authority, territorial organisation and sociopolitical cohesion, forming ritual-political hubs for early coastal societies. Some sites incorporated circular plazas (e.g. Cardal, Garagay), residential units (e.g. Mina Perdida) and infrastructure to control water flow (e.g. Manchay Bajo), suggesting the existence of inter-related ceremonial centres that fostered sociopolitical cohesion (Burger & Salazar 2023) and factional competition within a peer polity system (Renfrew & Cherry 1986; Brumfiel 2005; Erwin 2013).

Figure 1. Map showing the locations of U-shaped buildings in the Chillon, Rimac and Lurin valleys (figure by authors).

Infantas, a U-shaped complex in the Chillón Valley now encroached upon by the urban sprawl of Peru’s capital city, provides key insights into the mediation of power and ideology. The Chillón Valley contained at least seven U-shaped structures, with Infantas positioned in the lower valley alongside El Paraíso, Chuquitanta A and Chuquitanta B (Mesia-Montenegro 2024), paralleling the lower-valley concentration of complexes observed in the Rímac and Lurín valleys (Silva & García 1997).

Infantas

Identified in 1940s aerial photographs (Silva 1998), Infantas lies about 7km from the Pacific coast. Urban expansion has fragmented the complex into the central mound (Infantas I) and part of the left arm (Infantas II) (Figure 2). Excavations in 2008 revealed a monumental clay staircase, an atrium with white plaster flooring and adobe columns, all integral to the main mound. These features, though partially dismantled during Late Intermediate (AD 1000–1450) and Inka (AD 1450–1532) occupations, indicate that the complex was a significant ceremonial centre (Cornejo-Guerrero 2021).

Figure 2. Infantas: a) the Infantas complex and current urbanisation; b) reconstruction of Infantas (figure by authors).

Two excavation areas (AE-1 & AE-2) investigated the main mound (Figure 3). In AE-1, located at the summit, 12 excavation units of 2 × 2m were established. This area showed substantial disturbance due to looting and later occupations, predominantly yielding burials from the Late Intermediate and Inka periods. In contrast, the 12 × 1m trench in AE-2, situated on the north-east flank of the mound, revealed a well-preserved 30-step staircase leading to an atrium platform (Figure 4). The staircase, constructed with stone slabs bonded by mud mortar, closely parallels those found at Cardal and Mina Perdida (Burger & Salazar 2009).

Figure 3. Orthophotos of a) excavation units AE-1 and AE-2 at the main mound and b) excavation units at AE-2, note the staircase trench (figure by authors).

Figure 4. Views of the excavations at units AE-1 and AE-2, from above (a) and looking east (d), and an orthophoto (b) and excavation photograph (c) of the staircase trench excavations (figure by authors).

Excavation of the atrium in six 2 × 2m units uncovered column foundations and a white-plastered floor (Figure 5), architectural elements characteristic of Formative-period temples (e.g. Garagay and Mina Perdida; Ravines & Isbell 1975; Burger & Salazar 2009). The identification of conical adobe bricks further substantiates this affiliation, while scarce Formative-period fragments exhibit Janabarroid motifs (800–550 BC) (Figure 6), suggesting ties to Ancón and Garagay (Ravines et al. 1982; Rosas 2007). While limited in quantity, these parallels hint at broader interaction networks (Mesia-Montenegro 2024).

Figure 5. Atrium excavations: a) west view of grid 14 at AE-2, note the column base; b) north view of grid 14 at AE-2, note the column base (figure by authors).

Figure 6. Fragments of Formative ceramics retrieved from grid 14 at AE-2 (figure by authors).

Discussion

Strategic placement of U-shaped complexes in lower valleys marked control over agricultural and hydrological resources. U-shaped buildings also reflect environmental adaptation strategies. In the Lurín Valley, sites such as Manchay Bajo incorporated retaining walls to mitigate flood risks (Burger 2003). The strategic placement of Infantas indicates a similar integration of ceremonial and environmental functions in the Chillón Valley.

The presence of monumental staircases, atriums and columned spaces suggests a shared architectural expression among Formative-period sites in the Central Andes, while similarities in ceramics suggest interaction between contemporaneous sites. The central mound symbolically elevated authority, as seen in Cardal, Mina Perdida and Garagay, while plazas and staircases facilitated communal rituals (Moore 1996).

U-shaped complexes such as Infantas exemplify the concept of ‘embedded religiousness’, in which architecture, ideology and governance were deeply intertwined (Mesia-Montenegro & Sanchez-Borjas 2023). The construction of these monuments may have represented a fundamental component of religious practice, holding a significance comparable to the rituals and ceremonies performed within the completed structures.

The decline of U-shaped monumental traditions around 500 BC coincides with shifts in regional religious and political landscapes, including the rise of Chavín as a dominant religious centre (Mesia-Montenegro 2024), and with environmental disruptions linked to El Niño events (Sandweiss et al. 2009).

Conclusion

Infantas exemplifies the architectural, religious and sociopolitical significance of U-shaped monumental complexes during the Andean Formative period. Beyond its regional importance, Infantas serves as a compelling case study on the effects of modern urbanisation on archaeological sites worldwide; the entire right wing and 90 per cent of the left wing have been lost to urban expansion. Archaeological excavations played a pivotal role in securing legal protection for the site, leading to its designation as National Heritage.

Despite extensive destruction, surviving architecture confirms integration of the site within a broader ceremonial network. Future research, including radiocarbon dating and excavations at Infantas and other U-shaped complexes (Figure 1), will refine the chronology and regional connections of Infantas and the wider U-shaped architectural tradition.