Indus Valley civilization was mainly an urban culture sustained by surplus agricultural production and commerce, the latter including trade with Sumer in southern Mesopotamia. Both Mohenjo-Daro and Harappa are generally characterized as having "differentiated living quarters, flat-roofed brick houses, and fortified administrative or religious centers. The weights and measures of the Indus Valley Civilization, on the other hand, were highly standardized, and conform to a set scale of gradations. Distinctive seals were used, among other applications, perhaps for identification of property and shipment of goods. Although copper and bronze were in use, iron was not yet employed. "Cotton was woven and dyed for clothing; wheat, rice, and a variety of vegetables and fruits were cultivated; and a number of animals, including the humped bull, were domesticated,"Indus Valley civilization was mainly an urban culture sustained by surplus agricultural production and commerce, the latter including trade with Sumer in southern Mesopotamia. Both Mohenjo-Daro and Harappa are generally characterized as having "differentiated living quarters, flat-roofed brick houses, and fortified administrative or religious centers.