To present the Babylonian evidence, cuneiform texts and archaeological remains, for the Achaemenian rule over the satrapy Babairuš is to write a history of Mesopotamia. To write a history of Mesopotamia during these two hundred years would moreover necessitate the complete and critical utilization of contemporary and later classical sources. The cuneiform evidence of Achaemenian rule not only confirms the sequence of Persian rulers as known from Old Persian inscriptions and from Greek writers, but adds important chronological refinements. The student of Mesopotamian history can also rely on the inscriptions often written or stamped on bricks destined for temples, palaces, city walls, etc. In Mesopotamia as elsewhere historical events have left their imprints on literary creations and, conversely, literary creations have been used for political purposes. This chapter discusses the problems connected with the co-regency of Cyrus and Cambyses. Mesopotamian sources provide very little written evidence for Darius I, apart from the mention of his name in the Uruk kinglist.