Origin of writing
Among the necessary preliminaries for an advanced economy are weights and measures, writing and a legal system sufficient to both record and enforce contracts. The earliest known examples of full writing were pictographic and/or numerical and are found on clay tablets from Uruk dating to about 3100 BCE.
Before full writing, a system of clay tokens served similar functions in a more primitive manner. This fragment records a transaction which involves sheep and goats. The holes represent numbers and the animals are represented by pictographic signs.
Mesopotamian mathematics (including an illustration of the Pythagorian theorem predating Pythagoras by some 1250 years) also helped to provide the needed basis for accounting and economics (see this page on Mesopotamian Mathematics). This tablet including the square root of 2 provides evidence of the development of mathematics even higher than that required for commercial calculation.