sentences:  In the early 12th century the island along with Western Pomerania came under Polish suzerainty under Bolesław III Wrymouth, and became part of a newly formed vassal state of Poland, the Duchy of Pomerania.The Polish ruler initiated Christianization, entrusting this task to Otto of Bamberg, and in 1128 the Slavic Pomeranian Duke Wartislaw I was converted to Christianity through the efforts of Otto.In 1155 the Premonstratensians established a monastery in Grobe, generally known as Usedom Abbey, which in 1309 was moved to the village of Pudagla.