a river of Babylon, (Abydenus); called Pefsa Regia, the Royal Trench, or Cut (Polybius); the Royal River, (Ptolemy); Almarchar, (Pliny); Naarmalcha, (Ammonius); a factitious channel, or cut, made by Nebuchadonosor, and a horn or branch of the Euphrates, (Abydenus). The Euphrates naturally divides into two channels, one passing through Babylon, the other through Seleucia, and then falls into the Tigris; the factitious channel between these two is the Royal River; which mixes with the Tigris, a great deal lower down than Seleucia, at Apamea, (Ptolemy).