Calakmul is an ancient Maya site in the state of Campeche in Mexico. It is deep in the jungles of the Peten Basin area. It is 22 miles (35 km) from the border with Guatemala. Calakmul was one of the Maya lowlands’ biggest and most important ancient cities. Calakmul Structure 6 (or Structure VI) is on the west side of the Central Plaza. It makes up an E-Group astronomical complex with Structures 4a, 4b, and 4c. In 1989, observations proved that on March 21, the spring equinox, the sun rose behind Structure 4b, as seen from Structure 6. Image by Daniel Mennerich is licensed under CC BY-NC-ND 2.0.