Heavenly city

Oldest-known city in the Americas used astronomy to orient buildings.

The city of Caral, on Peru’s Supe Valley, flourished by 2600 BC, and is widely regarded as the oldest-known city in the Americas. The earliest powerful kingdom on the Pacific Coat, there were as many as 17 urban centres in the Supe region. Caral itself lies about 20km from the Pacific and 193km north of modern-day Lima.

Six large stone platforms with structures atop them built of quarried stone and river cobbles dominate the site, which also includes three sunken plazas and eight residential sectors of varying complexity. A small, but authoritative elite ruled Caral, at the time when Egypt’s Old Kingdom pharaohs were building the carefully orientated Pyramids of Giza. The Caral state was abandoned between 2000 and 1500 BC, for unknown reasons, just as other kingdoms came into prominence along the coast. But how was the site laid out?

Archaeologists Jose Ricra and Aldemar Crispin brought in Spanish experts – astro-astronomer Cesar Gonzalez-Garcia and astrophysicist Juan Antonio Belmonte. They measured 55 structures at 10 sites, including Caral and two centres nearer the ocean. Two main orientations emerged from the measurements. One was oriented toward the major lunar standstill, the other toward summer sunrise (December in the Southern Hemisphere). There is no way these orientations were random. Nor was a third, weaker orientation toward the siring of Sirius, the brightest star in the Southern Hemisphere. Thus, it is no coincidence that the first rays of the sun at the Summer Solstice enter through the stairs of Caral’s central pyramids and cross its main hall.

Perhaps the most important observation point was in one of the sunken plazas, where the person observing the solstice could be seen by a large crowd, thereby affirming the heavenly power of the elite. The summer solstice was especially important, for this was when the Supe River received mountain rainfall from the Andes.