A 60,000-strong crusading army gathered for an expedition against the pagan Prussians. The army included Bohemians and Austrians under the command of King Ottokar II of Bohemia, Moravians under Bishop Bruno of Olmütz, Saxons under Margrave Otto III of Brandenburg, and a contingent brought by Rudolph of Habsburg.

The Sambians were crushed at the Battle of Rudau, and the fort's garrison surrendered quickly and underwent baptism. The crusaders then advanced against Quedenau, Waldau, Caimen, and Tapiau (Gvardeysk); the Sambians who accepted baptism were left alive, but those who resisted were exterminated en masse. Samland was conquered in January 1255 in a campaign lasting less than a month. Near the native settlement of Tvangste, the Teutonic Knights founded Königsberg ("King's Mountain"), named in honor of the Bohemian king.