As the richest of the three rings, the Upper Ring contains the city's upper class population, as well as military and government officials. The most important citizens of the city reside here, protected against criminal activity by the presence of the Dai Li. The Royal Palace is located in the center of the Upper Ring, within its own walls. Aang, Katara, Sokka, and Toph received a home positioned in the Upper Class as a reward for their successful efforts against the Fire Nation's powerful drill and against the Fire Nation itself. The buildings of the Upper Ring are huge walled compounds, much like small versions of the Earth Kingdom Royal Palace itself, and the roofs are done with yellow tiles to symbolize the richness of the building and its owners. Obviously, Upper Ring Citizens are free to go wherever they please within Ba Sing Se, although it is best that they be careful when traveling to the Lower Ring as they may be the target of a crime.