Blessed Ceslaus, 0.P, (Polish: Czeslaw) was born in approximately 1180 in Kamien Slciski in Silesia, Poland, of the noble family of Odrowctz, and was a relative, possibly the brother, of Saint Hyacinth. Having studied philosophy at Prague, he pursued his theological and juridical studies at the University of Bologna, after which he returned to Cracow, where he held the office of canon and custodian of the church of Sandomierz.
About 1218 he accompanied his uncle Ivo, Bishop of Cracow, to Rome. Hearing of the great sanctity of Saint Dominic, who had recently been attributed the miracle of resuscitating the nephew of Cardinal Stefano di Fossa Nova who had been killed in a fall from his horse, Ceslaus, together with St. Hyacinth, sought admission into the Order of Friars Preachers.
In 1219 Pope Honorius ill invited Saint Dominic and his companions to take up residence at the ancient Roman basilica of Santa Sabina, which they did by early 1220. Hyacinth and Ceslaus along with their companions Herman and Henry were among the first to enter the studium of the Dominican Order at Rome out of which would grow the 16th-century College of Saint Thomas at Santa Maria sopra Minerva and the Pontifical University of Saint Thomas Aquinas, Angelicum in the 20th century. After an abbreviated novitiate Ceslaus, Hyacinth and their companions received the religious habit of the Order from St. Dominic himself in 1220.
Their novitiate completed, St. Dominic sent the young friars back as missionaries to their own country. Establishing a friary at Friesach in Austria, they proceeded to Cracow whence Ceslaus was sent by St. Hyacinth to Prague, the metropolis of Bohemia.
Labouring with much fruit throughout the Diocese of Prague, Ceslaus went to Wroclaw, where he founded a large priory, and then extended his apostolic labours over a vast territory, embracing Bohemia, Poland, Pomerania, and Saxony.
Sometime after the death of St. Hyacinth he was chosen the Provincial Superior for Poland. Whilst he was superior of the convent of Wroclaw all Poland was threatened by the Mongols. The city of Wroclaw being besieged, the people sought the aid of Blessed Ceslaus, who by his prayers miraculously averted the impending calamity. Four persons are said to have been raised to life by him. He died at Wroclaw on JuJy 15, 1242. In 1963, Pope Paul VI recognized Bl. Ceslaus - next to St. John the Baptist - as the main patron saint of the city of Wroclaw.
-taken from revolvy.com