Quintus Curtius Rufus, History of Alexander 9.9.10

9.9.10

quam torrentia praecipiti alveo incurrunt. Ignota vulgo freti natura erat, monstraque et irae deum indicia cernere videbantur, identidem intumescens mare et in campos paulo ante siccos descendere superfusum.

On the third day they observed that the sea, coming up with a tide as yet gentle, began to mingle its brine with the fresh water of the river. Then they rowed out to another island that lay in the middle of the river, making, however, slower progress in rowing since the stream of the river was now beaten back by the force of the tide. They put in to the shore of the island, and such as landed ran hither and thither in quest of provisions, never dreaming of the mishap which was to overtake them from their ignorance of tides. It was now about the third hour of the day when the ocean, undergoing its periodic change, rose in flood-tide, and began to burst upon them and force back the current of the river, which being at first retarded, and then more violently repelled, was driven upward contrary to its natural direction with more than the impetuosity of rivers in flood rushing down precipitous beds. The men in general were ignorant of the nature of the sea, and so, when they saw it continually swelling higher, and overflowing the beach which before was dry, they looked upon this as something supernatural by which the gods signified their wrath against their rash presumption.