Castro de Ulaca

Ulaca is the archaeological site of an iron age settlement in the province of Avila, Spain.

It was inhabitated by the Vettons, people of Indo-European origin that arrived in the Iberian peninsula during the second millenium B.C.

It was developed as a walled village on the top of a hill, at an altitude of 1500 m, during the 3rd-1st century B.C.

Several impressive remains are still visible today and some examples can be appreciated in the following 3D models:

- a stone quarry besides the foundations of a few houses

- a ritual sauna

- a sacrificial altar

Further down you can also find an analysis of the altar orientation and its possible astronomical meaning.

General view

This is a pictorial representation of the Ulaca village, on top of a hill and encircled by its wall.

Indicated in red are the locations of the 3D models acquired with the drone.

Source: Del Val y Escribano, Guía de lugares arqueológicos de Castilla y León, 2004.

The stone quarry

Certain areas were used as quarries, to carve stone blocks for construction.

The one acquired in this 3D model is located right beside a group of houses that were built with these blocks.

The drawing is taken from one of the description panels that are visible at the archaeological site.

Open th 3D model by clicking on the arrow and identify the quarry (1) and the foundations of a couple of houses (1 and 2).

The Sauna

This ruin has been interpreted as a ritual sauna. The rites might include the passage of a young man to the adult age, or the preparation for a fight.

A very evident feature in the ruin is a hole carved through the side wall. It was used to let the heat pass from an external fire place, to the internal chamber of the sauna.

The drawing is taken from one of the description panels that are visible at the archaeological site.

Open the 3D model by clicking on the arrow and identify the fire place (1), the lobby (2) and the main chamber (3).

The Altar

This ruin has been interpreted as an altar were rituals were performed.

It is carved in the rock, with two stairs to climb to the the top, and basins, to collect the blood and viscera of the victims sacrificed during the rituals.

To the side of the altar there is a rectangular area, probably a sort of lobby for those who were attending the ritual.

The drawing is taken from one of the description panels that are visible at the archaeological site.

Open the 3D model by clicking on the arrow an identify the main stair (1), the lateral stair (2), the basins (3) and the lobby (4).

This video is a virtual panorama around the digital model of the Altar:

The Altar astronomical significance

The lateral stair of the altar is somewhat anomalous because its first step is unusually high. When we extract the profile from the 3D model generated with the drone and take measurements we obtain that the first step of the lateral stair is one meter high and the stair inclination is 18º.

A one meter step is really impractical. Maybe this stair was not meant to climb to the top of the altar and had actually a different use…

The orthophoto generated with the drone, can be overlain in GoogleEarth and allows to analyse the orientation of the altar with respect to the surrounding landscape.

The altar is pointing towards a hill in the background, named “El Cuchillo”.

Its azimuth, with respect to the altar, is 32.5º to the east of the astronomical south.

The Winter solstice was a special date in the calendar of this ancient people.

The sun trajectory at winter solstice (December 21st) at the time of this people (400 BC) was reconstructed by means of the software “Stellarium”.

In the direction of “El Cuchillo” hill, the sun altitude over the horizon reached 18.5º.

This is practically identical to the inclination of the lateral stair of the altar (18º).

The Ulaca altar has been interpreted to have served as an astronomical observatory, to mark the occurrence of winter solstice.

That day, the steps of the lateral stair would remain in the shadow until the sun had reached the position above the “El Cuchillo” hill.

This theory was proposed by professor Manuel Pérez Gutierrez in: "Astronomy and Geometry in Vettonia" (2009).

The digital model of the altar obtained with the drone, integrated with the digital model of the topography, has allowed to test this theory analytically.