After a period of Norman rule, in 1189 the Kingdom of Sicily was in a succession dispute between Tancred, King of Sicily of an illegitimate birth and the Hohenstaufens, a German royal house, as its Prince Henry had married Princess Constance the last legitimate heir to the Sicilian throne. In 1191 Henry invaded Sicily after being crowned as Henry VI, Holy Roman Emperor and many cities surrendered, but Naples resisted him from May to August under the leadership of Richard, Count of Acerra, Nicholas of Ajello, Aligerno Cottone and Margaritus of Brindisi before the Germans suffered from disease and were forced to retreat. Conrad II, Duke of Bohemia and Philip I, Archbishop of Cologne died of disease during the siege. In light of this Tancred achieved another unexpected achievement during his counterattack that his contender Constance, now empress, was captured. He had the empress imprisoned at Castel dell'Ovo at Naples before her release on May 1192 under the pressure of Pope Celestine III. In 1194 Henry started his second campaign upon the death of Tancred, but this time Aligerno surrendered without resistance, and finally Henry conquered Sicily, putting it under the rule of Hohenstaufens.