Later Middle Ages Cologne's first Christian bishop was Maternus. He was responsible for the construction of the first cathedral, a square building erected early in the 4th century. In 794, Hildebold was the first bishop of Cologne to be appointed archbishop. Bruno I (925–965), younger brother of Otto I, Holy Roman Emperor, founded several monasteries here.
Later Middle Ages Cologne's first Christian bishop was Maternus. He was responsible for the construction of the first cathedral, a square building erected early in the 4th century In 794, Hildebold was the first bishop of Cologne to be appointed archbishop Bruno I (925–965), younger brother of Otto I, Holy Roman Emperor founded several monasteries here.