The Garden was 100 feet long by 100 wide and built up in tiers so that it resembled a theater. Vaults had been constructed under the ascending terraces which carried the entire weight of the planted garden; the uppermost vault, which was seventy-five feet high, was the highest part of the garden, which, at this point, was on the same level as the city walls. The roofs of the vaults which supported the garden were constructed of stone beams some sixteen feet long, and over these were laid first a layer of reeds set in thick tar, then two courses of baked brick bonded by cement, and finally a covering of lead to prevent the moisture in the soil penetrating the roof. On top of this roof enough topsoil was heaped to allow the biggest trees to take root. The earth was leveled off and thickly panted with every kind of tree. And since the galleries projected on beyond the other, where they were sunlit, they contained conduits for the water which was raised by pumps in great abundance from the river, though no one outside could see it being done. (Wellard, 1972, pp. 156)