In addition to the cathedral, the hill was also the site of other building work. The earliest evidence is of wooden structures dating from the 9th century, with the earliest stone buildings dating to the 10th and 11th centuries; the remains of the following buildings date from this era: the Rotunda of the Blessed Virgin Mary – probably from the turn of the 10th and 11th century; Church B (the earliest parts originate from the 10th century); Church of St Gereon (probably the palace chapel); the Church of St. George; the Church of St Michael; the Twenty-Four Pillar Room (possibly part of the Ducal Mansion); the Keep and the Residential Tower.