The Karkhaya Canal is said to have been dug at the time of the foundation of Baghdad by 'Isa, he being then occupied in building the famous mills at the junction of the Great Sarat and the Little Sarat, which will be described in the sequel. The Kasr 'Isa, the parent stream from which the Sarat and the Karkhaya were both derived, was one of the great navigable canals connecting the Euphrates with the Tigris, which dated from times long antecedent to Islam, having been dug by one of the Sassanian kings of Persia. The Karkhaya Canal meanwhile, after passing a place known by the curious name of the Mound of the Ass, sent off its single branch to the right, called the Kasr-al-Kilab, or the Dogs' Canal, which flowed out directly into the Kasr 'Isa, just below the Thorn Bridge.