He would not, however, return by the way he had gone, through the mountains, but he built ships on the river Jhelum, a tributary of the Indus, with which to coast along the shores to the mouth of the Euphrates.  There were forests of fir and pine to supply the wood, but their inhabitants, the apes and monkeys, collected in such force on the top of a hill near at hand, that the Greeks thought they were human enemies, and were about to attack them, till a native explained the mistake.