The Iliad 13.343–357

Thus were the two mighty sons of Cronos, divided in purpose, fashioning grievous woes for mortal warriors. Zeus would have victory for the Trojans and Hector, so giving glory to Achilles, swift of foot; yet was he in no wise minded that the Achaean host should perish utterly before the face of Ilios, but was fain only to give glory to Thetis and to her son, strong of heart. But Poseidon went among the Argives and urged them on, stealing forth secretly from the grey sea; for it vexed him that they were being overcome by the Trojans, and against Zeus was he exceeding wroth. Both the twain verily were of one stock and of one parentage, but Zeus was the elder born and the wiser. Therefore it was that Poseidon avoided to give open aid, but secretly sought ever to rouse the Argives throughout the host, in the likeness of a man. So these twain knotted the ends of the cords29.1 of mighty strife and evil war, and drew them taut over both armies,