With Nebuchadnezzar (604–561) began the colossal rebuilding of the entire city, with the restoration of the temple of Emach on the Citadel, of Esagila, of Etemenanki, the tower of Babylon with its wide temenos, of the Ninib temple in Ishin aswad, of temple “Z” and the earlier Ishtar temple in Merkes. He restored the Arachtu wall, constructed the earliest stone bridge over the Euphrates (p. 197) at Amran, the canal Libil-ḫigalla, that flowed round the Kasr on the north, east, and south, completed the Southern Citadel with his palace, and enlarged it towards the north in three successive extensions, in which the Procession Street was heightened and paved with stone, and the Ishtar Gate acquired its latest form, while both were decorated with the coloured enamelled frieze of animals. He built a new castle far out on the north and surrounded the city which he had enlarged in this fashion with the great outer city wall, of which from Homera we can see the white chain of mounds on the eastern horizon. Of Nabonidus (555–538) we have more especially the strong fortification wall on the banks of the Euphrates, that has been excavated from Kasr to the Urash gate, near the bridge at Amran (p. 200), and the Ishtar temple in Merkes. In the time of the Persian kings (538–331 B.C.), of which Artaxerxes II. (405–358) has left us a memorial in the marble building on the Southern Citadel (p. 127), the great change must have occurred that essentially altered the aspect of Babylon. The Euphrates, which until then had only washed the west side of the Kasr, now flowed eastward round the Acropolis. From this time dates the plan of the city as it is described by Herodotus (484–424? B.C.) and Ctesias, the physician of Artaxerxes. The apparently wide bend of the river that then flowed round the east of the Kasr we must now reconstruct in imagination as we look across to the castle of Nebuchadnezzar from Homera. Alexander the Great (331–323) set himself to prevent the decline of Babylon, which was then beginning, and to restore it to its former magnitude. The great tower Etemenanki, the sanctuary of Bel, and a marked feature of Babylon, was to have been rebuilt. The fallen masses were carried away, and the débris lies here in the mounds of Homera (p. 308), but the king died before he could rebuild the tower. From this time onward the burnt brick of the ancient royal buildings was re-used for all manner of secular buildings. The Greek theatre at Homera (p. 301) is built of such material. Thus the pillared buildings of Amran (p. 215 _et seq._) and houses at Merkes, that are built of brick rubble, belong either to the Greek (331–139 B.C.) or the Parthian (139 B.C.–226 A.D.) periods, but to which of them cannot be determined. At that time began the process of demolishing the city area, which perhaps was now only occupied by isolated dwellings, a process that certainly continued throughout the Sassanide period (226–636 A.D.).