Urban Geography studies the functions of cities and how urbanization has occurred historically and in different parts of the world. It analyzes the internal geography of cities and the distribution of housing, industry, commerce, and other functions. Early cities formed near dependable water supplies with fertile land and building materials where crops, trade, and defense were supported. Control of irrigation and religious authority were factors in ancient cities like Mesopotamia, while Greek and Roman cities organized public spaces and infrastructure that diffused across their empires. Medieval Islamic cities separated public and private domains while trade cities arose with globalization. Industrialization separated homes and workplaces with new urban forms and suburbanization emerging in modern times.