structural:expansion
Prehistory

When Ur was founded, the Persian Gulf's water level was two-and-a-half metres higher than today. Ur is thought, therefore, to have had marshy surroundings; irrigation would have been unnecessary, and the city's evident canals likely were used for transportation. Fish, birds, tubers, and reeds might have supported Ur economically without the need for an agricultural revolution sometimes hypothesized as a prerequisite to urbanization.