. During his life, Bolesław sponsored convents, monasteries and monks, especially the
Benedictines. Thanks to the intrigues of his wife,
Agnes of Babenberg, a half-sister of King Conrad III, Władysław II succeeded in convincing his brother-in-law to make a military expedition to Poland. The hastily organised expedition, however, clashed with the reluctance of the former subjects of the deposed high duke, and was finally defeated already on the Polish border near the
Oder river in August 1146. In subsequent years, Bolesław IV, along with his younger brothers, sought to maintain good relations with the royal
House of Hohenstaufen, Władysław's allies. To this end, in 1148 the junior dukes organized a meeting in
Kruszwica, to which they invited the warlike Margrave
Albert the Bear of the German
Northern March (the later
Margraviate of Brandenburg), who had reached the Polish border in the course of the
Wendish Crusade. There, Bolesław arranged the marriage of his sister
Judith with the margrave's son
Otto. Boleslaw and Mieszko also militarily supported the Germans in the fight against the reluctant West Slavic
Lutici tribes, considerably contributing to the stability of German domination over the middle
Spree region. The second important ally of the Piast prince was the
Wettin margrave
Konrad of Meissen. Initially, Bolesław also had a difficult relationship with another opposing force policy like the Hohenstaufens: the
Roman Curia under the
Pope Eugene III. At first, in 1147, the Papal legate Humbold recognised Bolesław as the new high duke and overlord of Poland. However, one year later, and again instigated by the intrigues of Władysław's wife Agnes, the newly appointed Papal legate Guy arrived in the country in connection with the refusal to restore the former high duke, and declared the ban over Poland. The penalty, thanks to the cohesive support of the Polish church hierarchy by the junior dukes, was virtually without repercussions. Things worsened for Bolesław in 1157, when King Conrad's nephew
Frederick Barbarossa, crowned
emperor by
Pope Adrian IV in 1155, decided to make a new expedition to Poland, thanks to the ongoing pressures by his aunt Agnes, Władysław's wife. This time, the campaign was well organised, and the Emperor was well determined to force Bolesław IV to accept his own conditions. It's unknown why Bolesław opted for a highly security tactics of war, not defending the swampy areas in front of the middle Oder river, which was for centuries the natural defense of Poland, nor the strongholds of
Głogów and
Bytom in Silesia. The Imperial army quickly advanced and soon laid siege to Poznan. Given the difficult situation, Bolesław was forced to accept the humiliating negotiations and, in a shameful ceremony on 30 August 1157, was declared a vassal of the Empire at his camp in
Krzyszkowo. Bolesław was on his knees and begged for forgiveness from the Emperor, in return for which he kindly received from Barbarossa the further control over the Polish lands; also, he had to pay an enormous tribute to the Emperor. For unknown reasons, however, despite Barbarossa's victory, Władysław II, to his great disappointment was not restored to the Polish throne. Bolesław formally swore loyalty to the Emperor on
Christmas Day in
Magdeburg, and gave his younger brother, Casimir II, as a hostage. Two years later, Władysław died in exile, having never returned to his country again. Not before 1163, the sons of the late Władysław,
Bolesław I the Tall and
Mieszko IV Tanglefoot, backed by the Emperor, insisting on the agreement made with Bolesław IV, were restored in their Silesia heritage; but this return didn't affect the power of Bolesław as a high duke. Thanks to its German affinities, the senior branch of the
Silesian Piasts at least managed to retain its Silesian lands (
Wrocław,
Legnica,
Głogów,
Opole and
Racibórz) without problems. == Crusade against the Prussians ==