Again, the earliest defensive bridges had another point in common with the primitive carpentry of Bhutan: they were made with tree-trunks resting on supports, and, when necessary, a part of their footways could be removed. Diodorus Siculus wrote a flaming account of a great bridge built by Semiramis over the Euphrates, rather more than two thousand years before the birth of Christ. After making due allowance for the frolicsome legends with which ancient history is enlivened, there are things worth noting in the enthusiasm of Diodorus. Herodotus attributed the same bridge not to Semiramis but to Nitocris, so evidence can be drawn from two authors. Pontists gather from the evidence that stone piers were connected by planks, which were taken up at night, just as the central part of a bridge in Bhutan could be removed as a military precaution. Diodorus draws entertaining pictures, and tries to prove that bridge-building was far advanced twenty centuries before our era began. If Semiramis collected architects and craftsmen from all the known civilizations, until at last she had at her beck and call a great host of capable servants, it is not surprising that she was able to build a fine bridge as well as to enlarge Babylon. The piers were grounded in deep water; their ends were protected by triangular buttresses; their stones were clamped together with thick bars of iron, which were soldered into the stones with molten lead. As for the superstructure, it was thirty feet wide, and all of wood--cedar, and cypress, and palm tree. In all this, probably, there is some exaggeration, but a famous bridge did exist at Babylon, and a combination of timber with stone piers was the most logical development from the simplest natural bridges--the fallen tree and the bridge of stepping-stones. Also it is likely enough that metal clamps were employed; iron was in vogue, and by using it in stonework under water an architect would feel less mistrustful of his cement and less anxious about the risks of floods. Further, it is quite probable that the entrance at each side was protected by a sort of drawbridge, because the times were lawless. Semiramis herself was put to death by her son Ninyas, and Ninyas in his turn was murdered.[119]