This volume publishes in full for the first time all known cuneiform manuscripts of an Akkadian calendar treatise composed in Babylon in the Late Babylonian period. Plates present hand-drawn copies of the damaged clay tablets in the British Museum’s Babylonian collection and the volume includes a composite edition and manuscript score. A comprehensive contextualizing introduction provides a key overview of topics in Mesopotamian scholarship, the manuscripts themselves, and their language and script. A detailed commentary explores how the treatise is unified by the theme of Babylonia’s invasion and how it aims to demonstrate the critical importance of the traditional Esagil temple in Babylon, its rituals, and its local elite for the security of Babylonia and its later imperial rulers.