After Conrad's death William of Holland received a certain allegiance, especially in the north of the country, and was recognized by the Rhenish cities which had just formed a league for mutual protection, a league which for a short time gave promise of great strength and usefulness. In January 1256, however, William was killed, and in the following year there was a double election for the German crown, Alphonso X., king of Castile, a grandson of Philip of Swabia, and Richard, earl of Cornwall, brother of the English king Henry III., being each chosen by parties of electors. Richard was crowned in May 1257, but the majority of his subjects were probably ignorant of his very name; Alphonso did not even visit the country over which he claimed to rule. The Teutonic Order in Prussia. During the reign of Frederick II. Prussia was conquered for Christianity and civilization by the knights of the Teutonic Order, who here built up the state which was later, in association with Brandenburg, deeply to influence the course of history. This work was begun in 1230. Knights eager to win fame by engaging in the war against the heathen Prussians flocked hither from all lands; towns, Königsberg, Thorn, Kulm and others, were founded; and in alliance with the Brothers of the Sword, the order was soon pressing farther eastwards. Courland and Livonia were brought into subjection, and into these lands also Christian institutions were introduced and German settlers brought the arts of peace. Period of Hohenstaufen dynasty.