波列斯瓦夫一世
After the Christianisations of the West Slavs in the 10th century, the state of the Polans was established and there were first attempts at conquering and baptizing the Baltic peoples. Bolesław I Chrobry sent Adalbert of Prague in 997 on a military and Christianizing mission. Adalbert, accompanied by armed guards, attempted to convert the Prussians to Christianity. He was killed by a Prussian pagan priest in 997.