A Vast Trade Network

Trade made cities possible and profitable. Mesopotamia lacked stone, timber, and metals, but its agricultural surplus could be exchanged for these materials.

Trade routes connected Sumer directly to the Indus Valley, Anatolia, and the Persian Gulf (Dilmun and Magan, in today's Bahrain and Oman). This created the world's first international economy, with standardized weights and measures, letters of credit, and commercial law. Sumerian goods even reached Egypt, though probably indirectly — passed along through Levantine middlemen such as the port of Byblos rather than by direct Sumerian voyages. The cities were not isolated experiments but nodes in a wide web of exchange.

Lapis lazuli from Afghanistan has been found in Sumerian tombs dated to 2600 BCE, proof of long-distance trade.