The Battle of Ostia, Raphael, 1514-15

The defense of Rome by Pope St. Leo IV against attacking Saracens in 847 is described by Voltaire:

Being attacked by the Saracens, Pope Leo IV showed himself, by his defence of Rome, worthy to rule there as a sovereign. He had employed the wealth of the Church in repairing the walls, building towers, and stretching chains across the Tiber. He armed the militia at his own expense, engaged the inhabitants of Gaeta and Naples to defend the shores and the port of Ostia, but did not neglect the prudent precaution of taking hostages from them, well knowing that those who are powerful enough to aid us are also powerful enough to injure us. He personally visited all the posts, and met the Saracens on their descent, not in warlike array, like Gozlin, Bishop of Paris, under circumstances still more urgent, but as a pontiff exhorting a Christian people, and as a king watching over the safety of his subjects. He was a Roman; in him the courage of the primitive ages of the republic was revived, in a time of cowardice and corruption, like some beautiful monument of ancient Rome that is sometimes found amidst the ruins of the new Rome. The Saracens were valorously met on their descent, and a tempest having scattered half their vessels, a portion of the invaders, who had escaped shipwreck, were captured and made to work in chains. Thus the pope utilized his victory by employing upon the defences and adornment of Rome the very hands which were to have destroyed her.