Sumerian economics

Imports
Discoveries of obsidian from far-away locations in Anatolia and lapis lazuli from Badakhshan in northeastern Afghanistan, beads from Dilmun (modern Bahrain), and several seals inscribed with the Indus Valley script suggest a remarkably wide-ranging network of ancient trade centered on the Persian Gulf. For example, Imports to Ur came from many parts of the world. In particular, the metals of all types had to be imported.

Trade
The Epic of Gilgamesh refers to trade with far lands for goods, such as wood, that were scarce in Mesopotamia. In particular, cedar from Lebanon was prized. The finding of resin in the tomb of Queen Puabi at Ur, indicates it was traded from as far away as Mozambique.

Slavery
The Sumerians used slaves, although they were not a major part of the economy. Slave women worked as weavers, pressers, millers, and porters.

Masonry
Sumerian potters decorated pots with cedar oil paints. The potters used a bow drill to produce the fire needed for baking the pottery. Sumerian masons and jewelers knew and made use of alabaster (calcite), ivory, iron, gold, silver, carnelian, and lapis lazuli.

Accounting and credits
Large institutions kept their accounts in barley and silver, often with a fixed rate between them. The obligations, loans and prices in general were usually denominated in one of them. Many transactions involved debt, for example goods consigned to merchants by temple and beer advanced by "ale women".

Financing
Commercial credit and agricultural consumer loans were the main types of loans. The trade credit was usually extended by temples in order to finance trade expeditions and was nominated in silver. The interest rate was set at 1/60 a month (one shekel per mina) some time before 2000 BC and it remained at that level for about two thousand years. Rural loans commonly arose as a result of unpaid obligations due to an institution (such as a temple), in this case the arrears were considered to be lent to the debtor. They were denominated in barley or other crops and the interest rate was typically much higher than for commercial loans and could amount to 1/3 to 1/2 of the loan principal.

Debt forgiveness
Periodically, rulers signed "clean slate" decrees that cancelled all the rural (but not commercial) debt and allowed bondservants to return to their homes. Customarily, rulers did it at the beginning of the first full year of their reign, but they could also be proclaimed at times of military conflict or crop failure. The first known ones were made by Enmetena and Urukagina of Lagash in 2400-2350 BCE. According to Hudson, the purpose of these decrees was to prevent debts mounting to a degree that they threatened the fighting force, which could happen if peasants lost the subsistence land or became bondservants due to the inability to repay the debt.