Born to the nobility. Benedictine monk at the Santa Giustina monastery in Padua, Italy. Chosen abbot in 1209 at age 24, he restored and expanded the abbey structure, and fought to maintain its rights. When Ezzelino III conquered Padua in 1237, Arnold escaped to Monselice. He returned in 1238, but when Ezzelino returned to the city, he arrested Arnold in 1246 and imprisoned him to live his remaining eight years on bread and water.