The left portal (Porte St-Jean) is an important survivor of the 12th-century Early Gothic period. The tympanum depicts the martyrdom of St. John the Baptist. In the lower register, Salome performs a balancing act (like a medieval jongleur) before King Herod, John is executed, and his head is presented on a platter. The upper register illustrates the legend that John was taken into heaven in ecstasy just before his death.

The present building comprises an aisled nave of 11 bays, with a series of aisle chapels, and an apsidal choir with an ambulatory and three spaced radiating chapels. The substantial transept arms are aisled on both sides, with large eastern chapels, and developed portals flanked by towers. A massive lantern tower lights the crossing. The two western towers, the Tour St. Romain (1160-1170) to the north and the Tour de Beurre to the south, flank the façade, rising beyond rather than above the western aisle bays. The south-west tower, the Tour de Beurre (so named because it was traditionally financed by a papal indulgence whereby people could eat butter during Lent provided they paid a fine to the building fund), was built by Guillaume Pontis and Jacques Le Roux between 1487 and 1507. The cathedral is still being restored after extensive damage in World War II. The only Romanesque remnant is the crypt, some re-used capitals and part of the Tour St. Romain. The current central spire (Tour Lanterne) is the highest spire in France, erected in 1876, a cast-iron tour-de-force rising 490 ft.