This is Constantine battling Maxentius at the Milvian Bridge. Supposedly, Constantine had a dream the night before the battle where a cross appeared to him saying he would win the battle. He did and legalized Christianity.
The School of Athens
Some say that Raphael snuck into see Michaelangelo's Sistine Chapel and was so impressed with the work that he changed his style and added Michaelangelo to the scene. He is the one on the lower left, sitting at the block of marble.