Here Christian, bishop of Prussia, who had received from the Polish duke of Masovia a part of Kulmerland as a fief, had founded the knightly Order of Dobrzin, and was attempting with its aid to subdue the heathens of Prussia.
Gave the Order the rights of a prince of the Empire in its territories: Conrad of Masovia gave it the whole of Kulmerland in 1230; while in 1234 the Order established its independence of all authorities except the Papacy, by surrendering its territories to the Holy See and receiving them back again as a fief.
The security of the kingdom was sensibly promoted by the erection of a cordon of fortresses on its north-eastern borders, and a blow was given to foreign interference when Casimir succeeded in gaining dominant influence over the independent Polish principality of Masovia, which had hitherto gravitated between Bohemia and the Teutonic Order.
But Masovia to the north, and Great Poland to the north-west, refused to recognize the supremacy of Little Poland, while Silesia soon became completely germanized.
In the first year of the 13th century, the Knights of the Sword, one of the numerous orders of crusading military monks, had been founded in Livonia to "convert" the pagan Letts, and, in 1208, the still more powerful Teutonic order was invited by Duke Conrad of Masovia to settle in the district of Kulm (roughly corresponding to modern East Prussia) to protect his territories against the incursions of the savage Prussians, a race closely akin to the Lithuanians.