Building J at Monte Alban at the Zapotec Site in Mexico

Keeping Track of Time at Monte Alban

Building J, Monte Alban (Mexico)
Building J, Monte Alban (Mexico). Hector Garcia

The mysteriously-shaped Building J at the Zapotec site of Monte Albán in the state of Oaxaca, Mexico, has been thought to have been built for astronomical and ritual purposes. Building J was likely first built about 1AD, with three main phases of construction, the most recent one between about AD 500-700.

Architectural Design 

The building has a roughly pentagonal outline and it is skewed 45% in orientation from the remainder of the buildings at the site by many degrees. The building is oddly shaped, and its shape been variously described as a baseball diamond, home plate, or arrowhead. Low relief carvings on the building include a crossed-sticks glyph, thought to represent astronomical symbols.

In addition to its remarkable exterior outline, it has a horizontal tunnel cut through it, and an outer staircase that's skewed another few degrees from the direction of the door.

Orientation and the Star Capella

Building J's architectural orientation is thought by researchers to point to the location of the star Capella. Capella is indicated by the orientation point of the building on May 2, when the sun reaches its zenith and passes directly overhead.

Also Known As: Monticulo J


There are more ancient observatories to read about; and more about Monte Alban and the Zapotecs as well.

Aveni, Anthony. 2001. Building J at Monte Alban. pp 262-272 in Skywatchers: A Revised and Updated Version of Skywatchers of Ancient Mexico. University of Texas Press, Austin.

Peeler, Damon E. and Marcus Winter 1995 Building J at Monte Alban: A correction and reassessment of the astronomical hypothesis. Latin American Antiquity 6(4):362-369.