The East Frieze on El Castillo.

The visible friezes are actually fiberglass replicas, as the originals are buried a few feet behind them in the walls of the pyramid, where they were discovered and excavated starting in the 1950s.

Apparently El Castillo was built up over time, perhaps with every 20 year cycle of the Mayan calendar; the previous exterior rooms and structures became entombed in the interior of the pyramid, while the structure itself grew taller and wider.

No evidence has been found of human sacrifice at El Castillo, but it certainly is possible.

The figure in this photo is thought to represent the Moon god.