A Bishop of Chur is first mentioned in 451/452 when Asinius attended the Synod of Milan, but probably existed a century earlier. According to local tradition, the first Bishop of Chur was St. Lucius, a reputed King of Britain, who is said to have died a martyr at Chur about the year 176, and whose relics are preserved in the cathedral. In the 7th century the bishopric acquired several territories south to the Lake of Constance. The see was at first suffragan to the archbishop of Milan, but after the treaty of Verdun (843) it became suffragan to Mainz. In 958 Holy Roman Emperor Otto I gave the bishopric to his vassal Hartpert with numerous privileges including control over the Septimer Pass, at the time the main pass through the central Alps. These concessions strengthened the bishopric's temporal power and later it became a princedom within the Holy Roman Empire.