The Consolation of Philosophy

Tigris and Euphrates f resolve themselves from one source,
And soon are separated by divergent waters.
If they should meet, and be called back again into one course,
That which the current of the alternate channel pulls along would flow together: g

Ships might come together, and trunks torn by the river,
And the mixed wave might entangle fortuitous modes:

...of the followers, and immediately those two rivers are separated by their divided waters. If they meet and are brought back into one course again, then what the water of each river carries will join; wherefore ships and trunks carried away by the river will meet, and the mixed waters will confuse...

f Tigris and Euphrates

The Tigris, so called for its speed due to its namesake, the arrow in the Persian tongue, is a river that rises in Armenia—if not from the same source, as the aforementioned Sallust says, at least from the same mountain from which the Euphrates rises. Then, washing the waves of Mesopotamia, it flows into the Euphrates, with which it flows into the Persian Gulf. Virgil speaks of this river (Eclogue 1, v. 62): "The Parthian shall drink the Arar, or Germany the Tigris, before I forget his face." The Euphrates, so named for the joy it brings to the inhabitants by fertilizing the fields with its flooding, is another river that rises from the same aforementioned mountains of Armenia. It fertilizes Mesopotamia with its floods, as the Nile does Egypt, and slips into the Persian Gulf with the added currents of the Tigris. Virgil spoke of this to signify the war of the Parthians, whose boundary was the Euphrates (Georgics I, v. 509): "Here the Euphrates, there Germany, stirs up war." I cannot omit what Quintus Curtius (Book V) says of both these rivers: "Those rivers," he says, "flow from the mountains of Armenia, and then, after a great divergence of waters, traverse the path they have taken, having covered two thousand five hundred stadia, which marked a most ample interval around the mountains of Armenia. When they began to cut through the lands of Media and the Gordians, they gradually come closer; and the further they flow, the narrower the space of land they leave between them. They are closest to those plains which the inhabitants call Mesopotamia. For they enclose Media on both sides. They burst into the Red Sea through the Babylonian territories."

g Current of the channel

They call a 'ford' (vadum) the water which, with banks not so far apart, can be crossed by foot, or on horseback, or at least by boat more easily than the sea: whence they think 'vadum' arises from 'vadendo' (wading), or from the Greek bathys deep/shallow, a place through which one wades. In French we say le gué, passer à gué; the lower Normans say le grand et le petit vé. That alternate channel or river, therefore, because it flows by the laws of nature, is carried along in such a known and certain course that it can be foreseen and intended by men; yet ships, trunks, and other bodies of that kind, which are carried surrounded by such waters, meet by a fortuitous or unexpected event.