The desire to define and purify doctrine, and to strengthen the Church, produced under a series of determined Popes a fierce outburst of persecution in the thirteenth century. In Milan, where heterodox opinions were held by many of the most powerful as well as the lesser citizens, it was the signal for repeated bouts of civil war and constant struggles between the Pope and the rulers of the city. The introduction of the Dominicans into Milan in 1220 gave an enormous advantage to the cause of orthodoxy. As soon as the people saw the Christ-like virtues of poverty and humility and evangelising ardour, hitherto associated in their minds only with the condemned Patarini, displayed by these approved Catholic orders, they followed the Friars with enthusiasm, careless indeed of doctrine, but believing and trusting those who lived as they did themselves and mingled with them freely, understanding their sorrows and needs. It is doubtful whether St. Dominic himself was ever in Milan, but his famous disciple, Peter of Verona, was sent there in 1232 by the Pope, with full authority to search out and punish heretics. Peter carried out his mission with merciless zeal. His name, made terrible by its unsparing use as authority for the infliction of torments and fiery death, came to be feared throughout Lombardy. So bitter a hatred did he rouse by his stern interpretation of the awful word, _not peace but a sword_, that he himself fell a victim to the weapon of his predilection. On a morning in 1252, as he was returning on foot with a single companion from Como to Milan, two assassins sprang out upon him from an ambush and smote him to death with a sword. The sword, transfixing his skull, is familiar to us all in mediæval and Renaissance art as the ornament and emblem of the Saintly Inquisitor.