We have come to the part of this siege which is told us in the _Iliad_, the oldest poem we know, except the Psalms, and one of the very finest. It begins by telling how Chryses prayed to Apollo to help him to get back his daughter, and Apollo sent a plague upon the Greeks in their camp. Calchas told them it was because of Chryseis, and they forced Agamemnon to give her safely back to her father.  His pride, however, was hurt, and he said he must have Briseis in her stead, and sent and took her from Achilles.  In his wrath Achilles declared he would not fight any more for the Greeks, and his mother Thetis begged Jupiter to withdraw his aid from them likewise, that they might feel the difference.