The vault itself was not a new feature. It was well known to Babylonian and to Assyrian builders, by whom it was used to cover spaces of narrow span.[93] Vaulted drains and tombs are of frequent occurrence, and Place found a barrel vault with a span of 4 metres in the gateways of Sargon’s palace at Khorsâbâd.[94] But though the principles of vault construction were familiar, the vault does not seem to have been developed to any notable extent before the second Babylonian empire at the earliest. Félix Thomas claims to have found the remains of monumental vaults in Sargon’s palace, but the proofs which he adduces are not convincing. There is no direct evidence for the domes which Place reconstructs over the rectangular chambers adjoining the temples, the area of the palace which was known in his days as the Harâm.[95] Layard found no trace of monumental vaults in his excavations of Assyrian palaces,[96] nor have any been discovered by the German excavators at Assur. Professor Koldewey is of opinion that the great hall at Babylon was vaulted, since, in the absence of all trace of columns, no other way of covering it is conceivable; and though direct evidence is not forthcoming, there is a strong likelihood that the proportions of the vault may have been greatly increased, and its structural value much more fully realized towards the end of the seventh or the beginning of the sixth century before Christ.[97] There are no data for its employment in Mesopotamia during the Hellenistic period, but it may safely be assumed that the absence of vaulted buildings in the eastern parts of the Seleucid kingdom is fortuitous. From the fourth century B.C. onwards western Asia shows a continuous series of cut stone vaults of small span,[98] many of which exhibit traits which point to their derivation from the sun-dried brick vaults of Assyria or from the cut stone vaults of the Saitic period in Egypt, themselves a derivation from sun-dried brick construction. In the second half of the third century, vaults with similar characteristics appear under Hellenistic influence in central Italy, where, after the middle of the second century, they underwent a development to which the Hellenistic East can offer no parallel.[99] At the end of the second century, while Latin builders threw their stone vaults securely over a span of 14·50 metres, as in the Ponte di Cecco in the Via Salaria, and even of 18·50 metres, as in the Pons Mulvius,[100] the Greeks of Asia Minor did not venture upon a span wider than 7·10 metres,[101] and confined themselves as a rule to vaults under 4 metres in span. It was now the part of the East to learn from Imperial Rome. Western Asia took back its own creation from the hands of Roman builders in the vast proportions which the proficiency of the latter had given to it, and over the whole of the Roman Empire the monumental vault sprang into being. The earliest extant examples on Mesopotamian soil are the