so after some discussions, Kalisz was exchanged with the town of Ołobok by Duke Przemysł II. Henry IV, High Duke of Poland On 30 September 1288, Leszek II the Black, Duke of Sieradz and High Duke of Poland, died without issue. This event opened an opportunity for Henry IV to realize his ambitious plans to gain Kraków and the title of High Duke. With this purpose, he began to find suitable allies from 1287, when he reconciled with Przemysł II, returning him Wieluń. According to the Professor and Historian Oswald Balzer, shortly before began the preparations to the First Coalition of Piast Dukes formed by Leszek II the Black, Henry IV, Przemysł II and Henry III of Głogow, which had the intention to make the unification of Poland. Notwithstanding the veracity of this theory, after hearing the news of Leszek II's death, Henry IV was ready for action. Henry IV's major contenders for the Kraków throne were Leszek II's half-brother Władysław I the Elbow-high and Duke Bolesław II of Płock, who counted on the support of the Lesser Poland nobility. However, the Duke of Płock failed to obtain the decisive support of the Castellan Sulk the Bear (Sułk z Niedźwiedzia), who was the Governor of the city. On 26 February 1289, the bloody Battle of Siewierz took place between the troops of the Dukes of Płock and Kuyavia, and Henry IV's troops, supported by King Rudolph I and the Dukes of Opole, Głogów and Ścinawa (Steinau). The battle ended with a victory for the Masovia-Kuyavia coalition; from two of Henry IV's allies, Duke Przemko of Ścinawa was killed in the battle, and Duke Bolko I of Opole was seriously injured and captured by Władysław I the Elbow-high. Despite this success, Duke Bolesław II of Płock unexpectedly resigned his pretensions, leaving all the Kraków inheritance to Wladyslaw I the Elbow-high. As the war turned favorable to him, Wladyslaw I, with the assistance of the Bishop of Kraków, Paul of Półkozic (who was later imprisoned after rebelled against him), managed to besiege and capture Wawel castle and forced the Silesian troops to retreat to Skała. However, Henry IV regrouped his forces and marched against Kraków in person at the head of his army in August 1289. Thanks to the betrayal of the Kraków townspeople and the help of the Franciscans (who even hid him in their monastery), Henry IV took the city