They say anyone can build a bridge that stands up, but it takes an engineer to build one that barely stands up. While this quote might be slightly exaggerating the engineering prowess of the average Joe, the fact is that building things accurately is difficult. The architectural and structural accomplishments of the Italian Renaissance are made all the more remarkable by the fact that instruments were imprecise and calculations had to be done by hand. What is even more impressive is when pre-modern structures are built with astronomical occurrences in mind. A prime example of this is El Castillo at Chichen Itza. This pre-colombian Mayan temple to Kukulkan, the Mayan serpet deity, was build to create an image of its god on the spring and fall equinoxes. On these days, the afternoon sun hits the northwest corner of the pyramid in such a way that the steps cast a serpent-like shadow along the northern staircase. This shadow runs the length of the staircase, connecting to the carved stone head of Kukulkan at the base.