992 AD Map of Poland in center showing some of Silesia Wroclaw Breslau already conquered by Poland Poland on and off conquered additional people s land surrounding Poland In 1157 the Holy Roman Empire ended the Polish conquest of Silesia by installing two Silesian duchies Wroclaw Breslau and Ratibor later named Lower Silesia and Upper Silesia The empire installed Boleslaus and Mieszko as dukes of Silesia who held both duchies in fief from the empire Even the Duchy of Poland the Polish dukes pledged allegiance to the empire and held territory as fief Only in 1025 did Boleslaw I Chrobry declare himself king and died the same year His son tried to evade taking the land in lien from the Holy Roman Empire but after some years had to submit Further Polish dukes all submitted to the empire Then Wenzel II a king of Bohemia part of the empire also became King of Poland Silesia conquered in the 990s by Boleslaw I Chrobry was until 1157 ruled by Polish dukes who were subject to the Holy Roman Empire Thus Silesia conquered in the 990s by Boleslaw I Chrobry was until 1157 Polish Map of Poland in 992 AD with Wroclaw Silesia partially conquered From 1157 Silesian dukes governed Silesia and they were subject to the highest dukes magnus dux of Silesia the Holy Roman Emperors