Arialdus, a deacon and martyr of the church of Milan, born near Milan in the first half of the 11th century, died in that city, June 28, 1066. He began to preach against the corruptions of the clergy at Milan about 1056. Aided by Landulphus, a young noble even more eloquent than himself, he aroused the popular feeling to such a degree that Pope Nicholas II. sent two legates to Milan to investigate the matter. They sustained Arialdus, but did not succeed in putting an end to the prevailing corruption. After the election of Pope Alexander II. the excitement again broke out at Milan, fomented by Arialdus and Erlembaldus, the brother of Landulphus. Pope Alexander excommunicated the archbishop of Milan, and reproved the other ecclesiastics. But even this did not conquer the abases; and although Arialdus continued to preach against them, the fickle Milanese became jealous of the attacks from Rome on their clergy. Taking advantage of this divided state of public opinion, his enemies had Arialdus assassinated on a desert island in Lake Maggiore. His name was enrolled in the list of martyrs by Alexander II.