Multi-level raised platforms, gigantic step-pyramids, corbelled roofs, and monumental stairways are all features of Maya architecture. The exteriors were embellished with sculpture and mouldings of Maya glyphs, geometric patterns, and religious symbolism, such as snake masks. Interiors were decorated with painted walls and sculptured stones. Maya architecture is known from the ancient cities of Chichén Itzá in Yucatán State, Mexico, and Uxmal in the western province of the same name. These two sites are among the most important archaeological treasures in Mexico. Hundreds of structures at Chichén Itzá have been identified by current research as administrative offices, ball courts, temples, and other public buildings used for royal ceremonies. At Uxmal, which was once the largest city in the Mayan world, the population probably exceeded 20,000. There are more than a thousand structures at this site, most of them large pyramidal temples built between AD 800 and 1000. During its peak, the city may have had a total population of 50,000 people. The Maya developed a new style of building construction that combined timber framing with stone masonry. This method allowed for larger structures with better protection against the elements than traditional brick or stone buildings. The Maya also used their knowledge of mathematics and astronomy to create an accurate calendar system based on a year of 360 days.