highest point of the cathedral. A south tower similar to the north tower was planned, and the base and buttresses for the tower were constructed, with walls two meters thick, next to the narthex, and a second level above, but it went no higher. Later in the 16th century The cathedral chapter decided to rebuilt the oratory to house a statue of the Virgin Mary rather than building the tower higher. The unfinished tower base reaches as far into the interior as the first traverse of the nave. A spiral staircase is encased in the massive stone construction. To the right of the north tower base are the vestiges of the chapel of Notre-Dame-des-Vertus, built in the 16th century but demolished in 1780. Nave and Choir The choir, built atop the Romanesque crypt, was begun first in about 1215, in a plan similar to another Burgundian church, Dijon Cathedral. The elevation has three levels; large arcades with pillars at the bottom; a narrow triforium, or passageway, above, with windowless arches and decoration by slender colonettes; and on the top level, double lancet windows below circular rose windows, with a narrow passageway along the wall at their base. The nave was originally planned to have a ceiling of six-part rib vaults, supported by alternating massive pillars and columns, but this plan was modified to have the more modern and stronger four-part rectangular rib vaults. Another notable architectural feature is the junction between the axial chapel at the east end with the disambulatory, the interior passage the surrounds the east end interior, allowing visitors to circulate while services were going on in the choir. In this disambulatory, the six-part vaults are supported by slender columns twenty-five centimetres in diameter, which give unity of style and animation to the end of the church. Crypt The crypt beneath the choir was constructed between by Bishop Hugues de Chalon, when he rebuilt the earlier Romanesque structure. It features an early disambulatory, allowing circulation by pilgrims around the tombs without disturbing services in the center. It contains the oldest art in the cathedral, including frescoes of Christ at the time of the Apocalypse commissioned by Bishop Humbaud, and a later fresco of Christ in Majesty from the end of the 13th century. Stained glass The cathedral has an important collection of 13th century stained glass. This includes some sixty windows made between 1235 and 1250, mostly