Chichen Itza was one of the largest Maya cities, with the relatively densely clustered architecture of the site core covering an area of at least 5 square kilometers. Smaller scale residential architecture extends for an unknown distance beyond this. The city was built upon broken terrain, which was artificially levelled in order to build the major architectural groups, with the greatest effort being expended in the levelling of the areas for the Castillo pyramid, and the Las Monjas, Osario and Main Southwest groups.
The site contains many fine stone buildings in various states of preservation, and many have been restored. The buildings were connected by a dense network of paved causeways, called sacbeob.[nb 4] Archeologists have identified over 80 sacbeob criss-crossing the site, and extending in all directions from the city. Many of these stone buildings were originally painted in red, green, blue and purple colors. Pigments were chosen according to what was most easily available in the area. The site must be imagined as a colorful one, not like it is today. Just like Gothic cathedrals in Europe, colors provided a greater sense of completeness and contributed greatly to the symbolic impact of the buildings.
The architecture encompasses a number of styles, including the Puuc and Chenes styles of the northern Yucatán Peninsula. The buildings of Chichen Itza are grouped in a series of architectonic sets, and each set was at one time separated from the other by a series of low walls. The three best known of these complexes are the Great North Platform, which includes the monuments of the Temple of Kukulcán (El Castillo), Temple of Warriors and the Great Ball Court; The Osario Group, which includes the pyramid of the same name as well as the Temple of Xtoloc; and the Central Group, which includes the Caracol, Las Monjas, and Akab Dzib.
South of Las Monjas, in an area known as Chichén Viejo (Old Chichén) and only open to archeologists, are several other complexes, such as the Group of the Initial Series, Group of the Lintels, and Group of the Old Castle.