Basilica or cathedral: what’s the difference?

Two words, two logics
The title of basilica rewards the importance of a sanctuary: its antiquity, its pilgrimage, its role in the history of the Church. It has nothing to do with the size of the building or its architecture. The word cathedral, on the other hand, is strictly administrative: it designates the church that houses the cathedra, the seat of the bishop of the diocese. A cathedral can be small, a basilica may not be a cathedral, and the reverse is also true.
Why Saint-Denis combines both
The building began as an abbatial church: it is the Abbey of Saint-Denis, led by Suger from 1122 to 1151, which invented the Gothic choir here, consecrated on 11 June 1144. In 1966, the creation of the Diocese of Saint-Denis turned this church into the cathedral of the new diocese, and it was granted the title of basilica. A single edifice, three successive statuses. The architectural history is on Suger and the first Gothic art.
What this means for your visit
A great deal, in fact. Since it is an active church, the nave is freely accessible without a ticket, and the monument closes during religious services. As it is a national monument, the royal necropolis requires a ticket to visit. This dual nature explains most failed visits, especially on Sunday mornings. See opening hours and closures and what is free.
Who decides what
The building is owned by the French State, and its monumental part is managed by the Centre des monuments nationaux; worship is overseen by the diocese. Two authorities, one roof, and overlapping schedules. The division is detailed on who owns the basilica.
On a Sunday morning, mass takes priority over visits. If you only have a morning, come on a weekday instead: see the best time to visit page.
Frequently asked questions
Is Saint-Denis a cathedral?
Yes, it has been the cathedral of the Diocese of Saint-Denis since 1966, and a basilica since the same year. See who owns the basilica.
Who grants the title of basilica?
The Pope. It is an honorary distinction, unrelated to the size of the building: see the largest basilica in France.
Can you attend a mass?
Yes, the nave is open and worship is conducted by the diocese; the monument is then closed to visitors. See opening times.