Casimir (Pol. Kazimierz), the name of several monarchs of Poland. I. The Peaceful, son of Miecislas II. and of Rixa, a German princess, died in 1058. After the death of his father in 1034 his mother ruled the country as regent; but the favors she bestowed upon her own countrymen, and their ill conduct, caused an outbreak of national hatred, and Rixa fled to Germany. Casimir followed her. Poland, left without a ruler, became a scene of the wildest anarchy and lawlessness; the lately established Christian church also suffered greatly from pagan persecutions. Profiting by this state of affairs, the Bohemians made an incursion into Poland, and advanced as far as Gnesen. In 1040 Casimir was recalled by his countrymen from Germany, where he was living in quiet retirement occupied with exercises of religious piety, which gained him the surname of "the Monk." Slightly assisted by Henry III. of Germany,, he regained his authority, and restored Christianity and a regular administration of justice, conquered Masovia, gained Bres-lau and other places from the Bohemians, and was honored with the title of restorer of Poland. His wife was Dobrogniewa, sister of Yaroslav, the grand duke of Kiev. His successor was Boleslas II. the Bold, his eldest son.

II. The Just, born in 1138, died in 1194. He was the voungest of the four sons of Boleslas III., among whom that monarch divided Poland, and reigned over the reunited country after the expulsion of Miecislas III. in 1177. He is greatly renowned for his personal virtues, as well as for the introduction of laws defending the peasants against the nobles and officers of the court. Under him the Polish senate was first organized, consisting of bishops, palatines, and castellans. He made successful expeditions to Volhynia, Halicz, and Lithuania.