sentences:  In 1458 Gregory entered the service of Albert of Austria and his opposition to papal authority was again aroused.Æneas Sylvius had ascended the papal throne as Pius II the same year, and soon afterwards (1459) summoned the princes of Christendom to Mantua to plan a crusade against the Turks.Gregory was present as the representative of Bavaria-Landshut, Kurmainz, and the Archduke Albert of Austria.