The Emperor Frederick, being encamped at Cerma, Alexander complained to him of the anti-pope, and received for answer, that they were both to go to him, and, having heard each side, he would determine which was the true pope.
This reply displeased Alexander; and, as he saw the emperor was inclined to favor the anti-pope, he excommunicated him, and then fled to Philip, king of France.

Frederick, in the meantime, carrying on the war in Lombardy, destroyed Milan; which caused the union of Verona, Padua, and Vicenza against him for their common defense.

About the same period the anti-pope died, and Frederick set up Guido of Cremona, in his stead.
The Romans, from the absence of the pope, and from the emperor being in Lombardy, had reacquired some authority in Rome, and proceeded to recover the obedience of those places which had been subject to them.
And as the people of Tusculum refused to submit to their authority, they proceeded against them with their whole force; but these, being assisted by Frederick, routed the Roman army with such dreadful slaughter, that Rome was never after either so populous or so rich.

Alexander now returned to the city, thinking he could be safe there on account of the enmity subsisting between the Romans and the emperor, and from the enemies which the latter had in Lombardy.

But Frederick, setting aside every other consideration, led his forces and encamped before Rome; and Alexander fled to William, king of Puglia, who had become hair of that kingdom after the death of Roger.