St. Michaels Tower, built during the late Saxon period in about 1040, is Oxfords oldest building. The tower formed part of the city wall with only fields and open countryside beyond to the north. The church tower was restored in 1986. Visitors to the tower are greeted in the first floor treasury by a magnificent display of rare silver, the earliest dated 1562, and the Charter of 1612 bearing the great seal of James I. Climbing the tower you will pass the interesting clock mechanism, the door to the martyrs' prison cell, a display of the Towers of the World, and the church bells before stepping out onto the roof of the tower to enjoy a panoramic view of the city and hills beyond. Entrance to the tower is through the glass Visitor Reception Centre. Structurally, the Church and Tower have remained largely unchanged since the fifteenth century, but both have undergone cosmetic improvements over the years.

The Tower was later connected on its west side to the Bocardo prison, above the North Gate. The three protestant bishops, Cranmer, Ridley and Latimer were held in the Bocardo prison before being taken in 1556 to be burned at the stake in Broad Street by Queen (Bloody) Mary. The door to their cell can be seen on display in the Tower. The North Gate was demolished in 1771 because it impeded the flow of traffic.