Ever since Cyrus had taken Babylon by turning the Euphrates out of its course, the ground had been ill drained, swampy, and unhealthy; and before setting out on further conquests, Alexander wished to put all this in order again, and went about in a boat on the canals to give directions.  His broad-brimmed hat was blown off, and lodged among the weeping willows round some old Assyrian’s tomb; and though it was brought back at once, the Greeks thought its having been on a tomb an evil omen, but the real harm was in the heat of the sun on his bare head, which he had shorn in mourning for Hephæstion.