Like their predecessors, the Mexica were dedicated observers of the sun, the stars, the cycles of nature, the passing of the seasons,and the death of plant and animal life. And like their predecessors, their architecture and their rituals were intended to maintain the integrity of the cosmic order. The science of observation was certainly very sophisticated,though it is still incompletely understood Templo mayor was constructed, however,so that it points about seven degrees south of east and that on the equinoxes, the sun rises exactly between the temples of Tlaloc and Huitzilopochtili. A monolithic Calendar stone, which is 1.2 meters thick, 3.6 meters in diameter, and weighing over 24 tons, was found in 1790 under the main square. On its face is a representation of the sun