Casimir I the Restorer
Bolesław I's expansive rule overstretched the resources of the early Polish state, and it was followed by a collapse of the monarchy. Recovery took place under Casimir I the Restorer (r. 1039–58). Casimir's son Bolesław II the Generous (r. 1058–79) became involved in a conflict with Bishop Stanislaus of Szczepanów that ultimately caused his downfall. Bolesław had the bishop murdered in 1079 after being excommunicated by the Polish church on charges of adultery. This act sparked a revolt of Polish nobles that led to Bolesław's deposition and expulsion from the country. Around 1116, Gallus Anonymus wrote a seminal chronicle, the "Gesta principum Polonorum", intended as a glorification of his patron Bolesław III Wrymouth (r. 1107–38), a ruler who revived the tradition of military prowess of Bolesław I's time. Gallus' work remains a paramount written source for the early history of Poland.