Named in Spanish El Caracol (the snail) for the spiral staircase inside its tower, the observatory at the Maya-Toltec site of Chichen Itza appears to be oriented toward a variety of celestial phenomena, viewed through its doors and windows. An unusual structure, with a round building on a square platform, it was built in the tenth century CE, late in the Classic Maya period (what’s called the Terminal Classic). The platform enables sky viewing over the surrounding vegetation. Its northeast–southwest axis is oriented to the summer solstice sunrise and the winter solstice sunset.
The central tower has partly collapsed, making it difficult to determine all of the observatory’s astronomical aspects. It is clear, however, that it was designed to trace the movements of the planet Venus with particular care. Venus was associated with a war deity, and it possible that one of the uses of the observatory was the planning of military activities. A grand staircase at the front of the building is – uniquely among Chichen Itza buildings – oriented to 27.5 degrees north of west, the northern extreme of the path of Venus.
Among the great Maya cities, Chichen Itza has a particularly extensive range of architectural elements, to which the observatory certainly contributes. The city is thought to have had an unusually diverse population, perhaps contributing to its variety of architectural styles.