The Basilica of St. Nazaire and St. Celse.

The Basilica of St. Nazaire and St. Celse or St. Nazarius and St. Celsus (Basilique Saint-Nazaire-et-Saint-Celse de Carcassonne), is a basilica minor in Carcassonne, southern France, listed as a national monument of the country.

It was formerly the cathedral of Carcassonne until 1801, when it was replaced by the present Carcassonne Cathedral(Cathédrale Saint-Michel de Carcassonne).

The present church is in origin a Romanesque of the 11th century, consecrated by Pope Urban II in 1096. It was built on the site of a Carolingian cathedral, of which no traces now remain. The crypt too, despite its ancient appearance, dates from the new construction. The church was enlarged between 1269 and 1330 in the Gothic style then predominant in France, largely at the expense of the Bishop of Carcassonne, Pierre de Rochefort.

The exterior was largely renewed by Viollet-le-Duc, while the interior has largely remained the Gothic original.

Carcassonne.

Carcassonne is a fortified French town in the Aude department, of which it is the prefecture, in the former province of Languedoc. It is separated into the fortified Cité de Carcassonne and the more expansive lower city, the ville basse. 

The fortified city itself is essentially of concentric design with two outer walls with towers and barbicans to prevent attack by siege engines. The castle itself possesses its own draw bridge and ditch leading to a central keep. The walls consist of towers built over quite a period. One section is Roman and is notably different from the medieval walls with the tell tale red brick layers and the shallow pitch terracotta tile rooves. One of these towers housed the Catholic Inquisition in the 13th Century and is still known as "The Inquisition Tower". Today there is a museum "Musée de la Torture", which shows some of the original torture equipment employed by the Catholic Church.

The newer part (Ville Basse) of the city on the other side of the Aude river (which dates back from the Middle Ages, created after the crusade) manufactures shoes, rubber and textiles. It is also the center of a major AOC wine-growing region. A major part of its income, however, comes from the tourism connected to the fortifications (Cité) and from boat cruising on the Canal du Midi. Carcassonne receives about three million visitors annually. – wikipedia