The Iliad 21.263–272

ever overtake Achilles for all he was fleet of foot; for the gods are mightier than men. And oft as swift-footed, goodly Achilles strove to make stand against him and to learn if all the immortals that hold broad heaven were driving him in rout, so often would the great flood of the heaven-fed River beat upon his shoulders from above; and he would spring on high with his feet in vexation of spirit, and the River was ever tiring his knees with its violent flow beneath, and was snatching away the ground from under his feet.