At the beginning of May the palm-groves of Assyria were reached. At Mazeprakt, where lay ruins of the enormous wall constructed by ancient Syrian kings, the enemy was seen for the first time. The Persians hastily retreated, and under a rain of poisoned arrows the Romans crossed the wide canal joining the Euphrates to the Tigris. This magnificent piece of engineering, made of Babylonian brick, cutting Mesopotamia in two, was called Nazar Malka, the River of Kings. Suddenly the Persians disappeared. The waters of the Nazar Malka rose, overflowed the banks, and flooded the vast surrounding plains. The Persians had organised the inundation by opening the sluices and dykes which lay on all sides, threatening the friable wastes. The foot-soldiers marched on, up to the knees in water, and their legs sank deep into mud. Entire companies disappeared into invisible ditches. Even horsemen and dromedaries with their burdens vanished suddenly. The track had to be sounded for with poles. The whole desert was transformed into a lake, and the palm-groves appeared like islands. "Whither are we going?" the cowardly began to murmur. "Why not retire at once to the river, and get on shipboard? We are soldiers; not frogs made for dabbling through mud!" Julian marched on foot with the infantry, even in the most difficult places. He helped to haul the labouring chariots out of mud-holes by their wheels; and laughed at his own soaked and clay-stained purple. Fascines and floating bridges were formed of palm stems; and at night-fall the army succeeded in reaching a dry place. The soldiers fell asleep, utterly exhausted. In the morning they saw the fortress of Perizaborh. From the tops of walls and inaccessible towers, spread with thick carpets and goat-skins, to defend them from the shock of siege-weapons, the Persians poured down scorn upon their enemies. The whole day passed in the exchange of insults and projectiles. Then, profiting by the darkness of a moonless night, the Romans, in absolute silence, carried the catapults and battering-ram from their ships (which had all this way accompanied the march) and propped these weapons against the walls of Perizaborh. The fosses were filled with earth, and by means of a _malleolus_, or enormous spindle-shaped arrow, full of an inflammable matter, made of pitch, sulphur, oil, and bitumen, the Romans succeeded in setting the goatskin carpets on fire.