The Song dynasty was an era of administrative sophistication and complex social organization. Some of the largest cities in the world were found in China during this period (Kaifeng and Hangzhou had populations of over a million). People enjoyed various social clubs and entertainment in the cities, and there were many schools and temples to provide the people with education and religious services. The Song government supported social welfare programs including the establishment of retirement homes, public clinics, and paupers' graveyards. The Song dynasty supported a widespread postal service that was modeled on the earlier Han dynasty (202 BCE – CE 220) postal system to provide swift communication throughout the empire. The central government employed thousands of postal workers of various ranks to provide service for post offices and larger postal stations. In rural areas, farming peasants either owned their own plots of land, paid rents as tenant farmers, or were serfs on large estates.