The population was structured around urban centres that had a range of different functions. Some were markets, while others were places where farm surpluses were stored. There were also political, administrative and military centres. The towns had streets that ran in straight lines or which followed to the lie of the land, had defensive walls around them and were evidently planned. The areas enclosed within the walls contained houses, stores, animal pens, manufacturing premises, places of worship and small, simple palaces. In the areas surrounding the towns and small cities, there was a large number of rural houses.