The square hole in the wall,Tulum Maya Ruins, served as an aperture for the sun to determine the two equinox.Within the precincts compound,was a marker, that when the sun's rays shown through the hole, aligned with a cross on the marker, it was equal hours of day and nights (equinox). Our Mayan guide indicated this occurred around 5:00 am, two times a year. * The Maya developed an original system of writing,with which they recorded astronomy,religion and history. The Maya also had a concept of zero. Civilization lasted 300BC to900AD. *Microsoft Encarta 99