Frederick II was excommunicated by Pope Innocent IV at the Council of Lyon. Rudolf sided against the Emperor, while the forest communities sided with Frederick. This gave them a pretext to attack and damage Neuhabsburg. Rudolf successfully defended it and drove them off. As a result, Rudolf, by siding with the Pope, gained more power and influence. Rudolf paid frequent visits to the court of his godfather, the Hohenstaufen emperor Frederick II, and his loyalty to Frederick and his son, King Conrad IV of Germany, was richly rewarded by grants of land. In 1254, he engaged with other nobles of the Staufen party against Bertold II, Bishop of Basle. When night fell, he penetrated the suburbs of Basle and burnt down the local nunnery, an act for which Pope Innocent IV excommunicated him and all parties involved. As a penance, he took up the cross and joined Ottokar II, King of Bohemia in the Prussian Crusade of 1254. Whilst there, he oversaw the founding of the city of Königsberg, which was named in memory of King Ottokar. Rise to power The disorder in Germany during the interregnum after the fall of the Hohenstaufen dynasty afforded an opportunity for Count Rudolf to increase his possessions. His wife was a Hohenberg heiress; and on the death of his childless maternal uncle Count Hartmann IV of Kyburg in 1264, Rudolf seized Hartmann's valuable estates. Successful feuds with the Bishops of Strasbourg and Basel further augmented his wealth and reputation, including rights over various tracts of land that he purchased from abbots and others. These various sources of wealth and influence rendered Rudolf the most powerful prince and noble in southwestern Germany (where the tribal Duchy of Swabia had disintegrated, enabling its vassals to become completely independent). In the autumn of 1273, the prince-electors met to choose a king after Richard of Cornwall had died in England in April 1272. Rudolf's election in Frankfurt on 1 October 1273, when he was 55 years old, was largely due to the efforts of his brother-in-law, the Hohenzollern burgrave Frederick III of Nuremberg. The support of Duke Albert II of Saxony and Elector Palatine Louis II had been purchased by betrothing them to two of Rudolf's daughters. As a result, within the electoral college, King Ottokar II of Bohemia (1230–1278), himself a candidate for the throne and related to the late Hohenstaufen king Philip of Swabia (being