Frederick, however, withdrew from Rome on account of the plague which then prevailed, and returned to Germany.
The cities of Lombardy in league against him, in order to command Pavia and Tortona, which adhered to the imperial party, built a city, to be their magazine in time of war, and named in Alexandria, in honor of the pope and in contempt of Frederick.
Guido the anti-pope died, and Giovanni of Fermo was appointed in his stead, who, being favored by the imperialists, lived at Montefiascone.
Pope Alexander being at Tusculum, whither he had been called by the inhabitants, that with his authority he might defend them from the Romans, ambassadors came to him from Henry, king of England, to signify that he was not blamable for the death of Thomas a Becket, archbishop of Canterbury, although public report had slandered him with it.

On this the pope sent two cardinals to England, to inquire into the truth of the matter; and although they found no actual charge against the king, still, on account of the infamy of the crime, and for not having honored the archbishop so much as he deserved, the sentence against the king of England was, that having called together the barons of his empire, he should upon oath before them affirm his innocence; that he should immediately send two hundred soldiers to Jerusalem, paid for one year; that, before the end of three years, he should himself proceed thither with as large an army as he could draw together; that his subjects should have the power of appealing to Rome when they thought proper; and that he should annul whatever acts had been passed in his kingdom unfavorable to ecclesiastical rule.

These terms were all accepted by Henry; and thus a great king submitted to a sentence that in our day a private person would have been ashamed of.

But while the pope exercised so great authority over distant princes, he could not compel obedience from the Romans themselves, or obtain their consent that he should remain in Rome, even though he promised to intermeddle only with ecclesiastical affairs.
About this time Frederick returned to Italy, and while he was preparing to carry on new wars against the pope, his prelates and barons declared that they would abandon him unless he reconciled himself with the church; so that he was obliged to go and submit to the pope at Venus, where a pacification was effected, but in which the pope deprived the emperor of all authority over Rome, and named William, king of Sicily and Puglia, a coadjutor with him.

Frederick, unable to exist without war, joined the crusaders in Asia, that he might exercise that ambition against Mohammed, which he could not gratify against the vicars of Christ.