A phase in Mesopotamia when cuneiform documents provide dates for significant events in relation to a given year in a king's reign. Dating by year formula, done from Akkadian through Old Babylonian times, provides a basic framework for the political history of southern Mesopotamia. The Assyrians did not, unlike the Babylonians, use year formulas containing interesting historical details; instead, every year was designated by the name of a high official (eponymic dating). The reconstruction of Hammurabi's rule is based mainly on his date formulas; years were named for a significant act the king had performed in the previous year or at the beginning of the year thus named.