The earliest known urban culture of the Indian subcontinent, identified in 1921-1992 by its two capitals - Harappa and Mohenjo-Daro - both in modern Pakistan. It was also the most extensive of the three earliest civilizations, the other two being Mesopotamia and Egypt. It was one of the greatest civilizations of antiquity, but its origins are obscure. By around 2300 BC, the Indus civilization was fully developed and in trading contact with Sargonid Sumer. Radiocarbon dates from several sites support an origin c 2600 BC, and suggest that by 2000 BC the civilization was in marked decline. The Indus River seems to have played a significant part, as many sites show deposits left by frequent catastrophic floods. Exploitation of the vegetation, particularly for the baking of enormous quantities of brick, caused the decline of the countryside. The final collapse seems to have been due to hostile attack. A few inhumation cemeteries have been found associated with the gridiron-plan cities and there were elaborate drainage systems, also. The site of Mohenjo-Daro had a great bath, assembly hall, and other monumental buildings. There was widespread use of an undeciphered hieroglyphic script and standard weights and measures. The economy was based on mixed agriculture and humped cattle were the most important domestic animals. The pottery was mass-produced and plain. Artistically the finest products were square steatite seals, carved with local or mythical animals and brief inscriptions. The civilization's effect on the later culture and religion of India seems to have been considerable.