Diodorus Siculus, a Greek historian, stated that the platforms on which the garden stood consisted of huge slabs of stone (otherwise unheard of in Babel), covered with layers of reed, asphalt and tiles. Over this was put "a covering with sheets of lead, that the wet which drenched through the earth might not rot the foundation. Upon all these was laid earth of a convenient depth, sufficient for the growth of the greatest trees. When the soil was laid even and smooth, it was planted with all sorts of trees, which both for greatness and beauty might delight the spectators."
How big were the gardens? Diodorus tells us they were about 400 feet wide by 400 feet long and more than 80 feet high. Other accounts indicate the height was equal to the outer city walls, walls that Herodotus said were 320 feet high. In any case the gardens were an amazing sight: A green, leafy, artificial mountain rising off the plain.