Inca Masonry Secrets Revealed as Coricancha Wall Replicas Collapse on Cue in Lab Tests

The stones of the Coricancha, the Inca temple that once anchored the imperial capital of Cusco, have stood through nearly five centuries of earthquakes without a drop of mortar binding them together. Now a team of Peruvian and European engineers has brought that masonry into the laboratory, toppling carefully built replicas on a tilting table to find out exactly when and how such walls fail. Their study, published in the Bulletin of Earthquake Engineering, shows that relatively simple computer models built from rigid blocks can predict the collapse of dry-jointed stone walls with striking accuracy, offering a new tool for protecting some of the world’s most vulnerable heritage structures.

Dry-joint stone construction, in which precisely shaped blocks are stacked without mortar, is found across the globe, from Inca Peru to ancient Greek fortifications and medieval retaining walls. The technique produces remarkably durable structures, but it also leaves them with a fundamental weakness: with nothing gluing the stones together, the walls depend entirely on gravity and friction for their stability. When an earthquake shakes a wall perpendicular to its face, a loading direction engineers call out-of-plane, the blocks can slide, rock and ultimately overturn in a cascade of falling stones. Understanding the threshold at which that overturning begins is one of the central problems in the seismic assessment of historic masonry.

The research team, led by Leonel Lipa of the Pontificia Universidad Católica del Perú and Universidad San Ignacio de Loyola, together with Nicola Tarque of the Universidad Politécnica de Madrid and Luca Pelà of the Universitat Politècnica de Catalunya, chose one of the most iconic examples of the technique as their template. The Coricancha temple, whose polished stone walls later formed the foundations of the convent of Santo Domingo, is celebrated for its trapezoidal openings, gently inclined wall faces and joints so tight that a knife blade cannot slip between the blocks. Reproducing those characteristics at reduced scale was the first challenge of the project.

Rather than carving scarce and protected andesite, the researchers cast concrete blocks whose geometry and arrangement mirrored a section of the Coricancha’s dry-jointed stonework. Three walls were built at 1:2 scale, each following the block layout, aspect ratios and construction details of the original heritage fabric as closely as the material substitution allowed. The concrete mix was characterised through a battery of standardised tests covering compressive strength, density and aggregate properties, so that the mechanical inputs to the numerical models rested on measured values rather than assumptions. Building the replicas block by block also meant that every joint in the test walls corresponded to a joint in the real structure, preserving the discontinuous nature that governs how these assemblies move.

The test rig was a tilting table, a device that slowly rotates a platform on which the wall stands until gravity’s effective direction tilts away from vertical. This pseudo-static approach is a well-established way to probe out-of-plane stability: as the table inclines, the wall experiences an increasing horizontal component of its own weight, mimicking the lateral forces an earthquake would impose. The researchers tilted each of the three walls until collapse, recording the angle at which the structure first showed visible movement, the sequence of block displacements that led to failure, and the final angle at which overturning became irreversible. These pre-collapse drifts, collapse mechanisms and collapse angles form the experimental benchmark against which any numerical model must be judged.

What the tests revealed was a consistent pattern of behaviour. The walls did not crumble randomly; instead they developed well-defined failure mechanisms in which portions of the masonry separated along joint lines and rotated as coherent groups of blocks. This is the hallmark of dry-joint masonry: because the blocks carry almost no tensile strength across their joints, deformation concentrates in the interfaces, and the wall behaves less like a continuous solid and more like an assembly of rigid bodies pushing against one another. Capturing that behaviour numerically is difficult for conventional finite element codes, which are built around continuous materials and can struggle with the opening, closing, sliding and impacting of many separate contact surfaces.

The team’s answer was a hybrid approach that embeds rigid-body mechanics within a finite element framework. In this formulation, each stone is idealised as a rigid block, an idealisation justified by the fact that the stresses within individual stones remain far below the material’s strength, so the blocks themselves barely deform. All of the action happens at the joints, where the model accounts for contact, friction and the small local deformations that occur where two stone faces meet. The numerical simulations were set up with the geometry of the scaled walls and the measured material and interface properties, then subjected to the same progressive tilting as the physical specimens.

The agreement between experiment and simulation was the study’s decisive result. The numerical models accurately predicted the collapse angles at which the walls overturned, reproduced the experimentally observed failure patterns, and matched the average drift measured at various inclination angles throughout the loading history. In other words, the models did not merely get the final failure threshold right; they tracked the wall’s response along the way, capturing how the structure leaned, cracked open along its joints and redistributed its weight as the tilt increased. That level of fidelity matters, because a model that only matches the collapse angle could do so for the wrong reasons, while one that reproduces the full deformation path gives engineers genuine confidence in its predictions.

For heritage custodians, the implications are immediate. Structures like the Coricancha cannot be instrumented, loaded or dismantled to assess their safety, so any evaluation must rely on numerical analysis. A validated modelling strategy means engineers can now build a digital twin of a real Inca wall, using its surveyed geometry and representative material properties, and estimate with quantified confidence how close it sits to overturning under the seismic demands of a region as earthquake-prone as the Peruvian Andes. The approach also opens the door to testing hypothetical interventions digitally, allowing conservators to compare strengthening options before committing to any physical alteration of protected fabric.

The work also fits into a broader research effort by the same groups, who have previously applied rigid-body dynamics to the colossal terraced walls of Sacsayhuamán above Cusco and developed a taxonomy of pre-Hispanic stone wall types in southern Peru. By anchoring the new models to physical experiments on faithful scaled replicas, the team has closed the loop between field observation, laboratory evidence and computational prediction. The dataset from the study has been released in the Zenodo repository so that other researchers can scrutinise and extend the results. As seismic risk grows across the mountainous regions where dry-stone heritage concentrates, the image of three concrete replicas of an Inca temple wall toppling on cue in a Lima laboratory may prove to be a turning point: the moment the ancient builders’ empirical mastery of friction and gravity finally became something modern engineering could simulate, verify and defend.

Subject of Research: Out-of-plane seismic behaviour and rigid-body numerical modelling of historical dry-joint stone walls based on scaled Coricancha temple replicas

Article Title: Experimental and numerical analysis of out-of-plane behaviour of historical dry-joint stone walls: insights from a scaled laboratory wall model of the Coricancha temple, Peru

Article References: Lipa, L., Tarque, N., Goicolea, J. M., Santa-Cruz, S., Quispe, L., Pillaca, E., & Pelà, L. (2026). Experimental and numerical analysis of out-of-plane behaviour of historical dry-joint stone walls: insights from a scaled laboratory wall model of the Coricancha temple, Peru. Bulletin of Earthquake Engineering. https://doi.org/10.1007/s10518-026-02710-7

Image Credits: AI Generated

DOI: 10.1007/s10518-026-02710-7

Keywords: dry-joint masonry, out-of-plane behaviour, Coricancha temple, Inca architecture, rigid body dynamics, finite element method, tilting table test, collapse mechanism, heritage structures, seismic assessment, scaled wall model, earthquake engineering