-set
vault, that we have already encountered in Egypt.[280] The chamber figured
below is taken from the necropolis of Mugheir, formerly "Ur of the
Chaldees." It is built of crude brick bound with mud. The vault is
supported by walls sloping upwards and outwards like those of a modern
tunnel (Fig. 89).[281]

Such a method of construction is only adapted to buildings of small
dimensions; it could not be used for chambers with wide roofs, or where any
great weight was to be upheld. The arches upon which, according to both
Strabo and Diodorus,[282] the hanging gardens of Babylon were supported,
must have been real centred arches. As to whether they were of pise, like
those of Khorsabad, the Greek writers tell us nothing. From what we know of
the habits of the Chaldaean builder we may conclude that they were true
arches with voussoirs either of bricks burnt in the kiln, or so well dried
that they were almost as hard and durable as those that had passed through
the fire. This conjecture is confirmed by the fact that the structures in
question lasted till the Macedonian conquest. Strabo and Diodorus speak of
the great temple of Bel as so ruinous that its original height could not be
guessed, even approximatively. It was otherwise with the hanging gardens.
Of these they give the measurements, on plan, of the platforms and piers,
together with their heights, and the heights of the arches. We should find
it difficult to explain the preciseness of these measurements and their
agreement one with another, unless we supposed that both writers had some
exact authority, such as one of the companions or historians of Alexander,
to refer to. The kings of Persia lived at Babylon for a part of the year.
These princes may well have been indifferent to the preservation of the
national fanes, they may even have hastened their destruction, as Xerxes is
said to have done, in order to punish and humiliate the rebellious
Babylonians. But in their own interest they would see that proper care was
taken of those hanging gardens by which their stay in the city would be
rendered more pleasant than it would otherwise have been, from whose lofty
platforms their watchful eyes could roam over the city and the adjoining
plain, and follow the course of the great river until it disappeared on the
south amid groves of waving palm. After the rise of Seleucia and Ctesiphon,
however, the gardens would rapidly hasten to decay, but they must have been
solidly built