The most important center of the Mexican highlands after the fall of Teotihuacan was Cholula, near the twin volcanic peaks Iztaccihuatl and Popocatepetl and the city of Puebla. The Great Pyramid there, dedicated to Quetzalcoatl, is the largest single structure in the New World. Towering 181 feet high and covering an area of some 25 acres, the pyramid was begun in Pre-Classic times and enlarged four times. Seen from a distance today, it appears to be a large hill with a Colonial church resting at its summit. The interior of the pyramid has been extensively excavated, affording visitors an extraordinary opportunity to view the different phases of its construction.