18 And concerning the third beast he said that it was like a leopard, and it had four birds' wings on its back and that beast had four heads. Now this third beast was Alexander the Macedonian. For he was strong as a leopard. And as for the four wings and the four heads that the beast had, that was because he gave the kingdom to his four friends to govern after him, when he had come and slain Darius and reigned in his stead.
Source: Demonstrations (New Advent)