The gradual raising of the buildings on the Kasr and their development into the Acropolis of Babylon may be classified in their principal features under the following periods: 1. The wall of the river bank built by Sargon. Imgur-Bel and Nimitti-Bel, the walls connected with it, no longer exist. 2. Nabopolassar’s palace of mud brick on a foundation of burnt brick, surrounded by an enclosing wall which included the _irṣit Babil_ and to which the arched door belongs. Building of the Arachtu walls in three successive periods. 3. Nebuchadnezzar replaced the mud brick of his father by walls of burnt brick, restored the enclosing wall, built the older moat wall, and renewed the Ninmach temple of Sardanapalus. 4. Building of the two mud walls, which may prove to be Imgur-Bel and Nimitti-Bel, and in which stood the ancient Ishtar Gate, which no longer exists. 5. Building of the east part of the Southern Citadel. Raising of the enclosing wall, of the Ninmach temple, and of the Procession Street. 6. Rebuilding of the Ishtar Gate with the brick reliefs, and heightening of the two mud-brick walls. 7. Construction of the moat wall of Imgur-Bel. Raising of the Nabopolassar palace. 8. Extension of the palace to the west. The whole Southern Citadel now lay on the higher level. Completion of the southern water arm (Libil-ḫigalla?), which also encircled the Southern Citadel in the east. 9. Project for an advanced building in the north, of which the 17–metres-thick wall in the Principal Citadel is part. 10. Building of the Principal Citadel, with the two parallel walls that flank the Procession Street and the two wall lengths that turn east and west. Raising of the Procession Street and stone pavement, of the Ishtar Gate with the enamel reliefs, and of the Ninmach temple. 11. Lengthening of the parallel walls to the north. Building of the flanking walls and the stone wall. 12. Neriglissar’s and Nabonidus’ restorations, of which there are scanty traces. 13. Uniting of the entire Kasr by means of the Persian advanced wall of the Acropolis, after the Euphrates had removed its channel to the east side. Building of a palace on the western Southern Citadel by Artaxerxes Mnemon. 14. In the Parthian period the downfall and demolition began. Houses of burnt brick and brick graves among the ruins. The Euphrates returned to its ancient bed. 15. A large necropolis of late Parthian or Sassanide times in the principal court of the Southern Citadel. It must be admitted that these epochs cannot be always clearly differentiated. They form only an approximate sketch of the development so far as it has hitherto been possible to recognise it, and for some time to come will require emendation and amplification. XXX THE PERIBOLOS OF ETEMENANKI