Sylvester IV was a claimant to the papacy from 1105 to 1111.
Members of the Roman aristocracy, with the support of the German king Henry V (1105–25) set up another antipope to replace Pope Paschal II (1099–1118), electing Maginulfo, the Archpriest of St. Angelo in Peschiera, while Paschal II was outside of Rome. After his election, Maginulfo took the papal name of Sylvester IV and was consecrated in the Church of St. Maria Rotonda (the Pantheon) and was enthroned in the Lateran on November 18, 1105. When Paschal II returned to Rome the next day, Sylvester IV left for Tivoli and finally settled in Osimo, Province of Ancona, under the protection of Count Guarniero di Ancona. On April 11, 1111, Paschal II and King Henry V reached an agreement about the investiture of Catholic bishops. Then the king, who had used Sylvester IV to exercise pressure on Paschal II, made the antipope abandon his claim to the office of pope and submit to Paschal II. He was allowed to live out the rest of his life in Ancona with Count Guarniero, his patron.