of course its not the main theater in modern rome, but at the time of Augustus, the succesor to Julius Ceaser, this was the theater that held all the important performances, and was until the colosseum the largest of all theaters in rome. this theater because of its stlye often is confused with the colosseum, but you can see how this one is much smaller, and was only a half circle, where as the colosseum is much larger and an oval.