Saint-Florent Cathedral or Nebbio Cathedral (Cathédrale Santa-Maria-Assunta, also known as Cathédrale du Nebbio) is a former Roman Catholic church located in the town of Saint-Florent in Corsica, France. The cathedral is a national monument and is now the church of Santa Maria Assunta.
The was the seat of the Bishop of Nebbio until 1801, when the diocese was merged into the Diocese of Ajaccio.
The ancient region of the Nebbio, or Nebbiu, on Corsica formed a Christian bishopric from the 5th century onwards. The former cathedral, now the church of Santa Maria Assunta, located at the edge of the town of Saint-Florent on the road that leads to Poggio d'Oletta, is a heavily-restored Romanesque structure. The date of its construction is put at between about 1125 and 1140. The building has had protected status since 1840 and been classed as a national monument since 1875.
The first clear documentary reference to this cathedral is in a deed dated 1176 transcribed in the cartulary of Calci Charterhouse, although it may well be referred to in two earlier documents of 1138 and 1145.
Because of the insecurity of the coasts and the malaria which was endemic in the marshes that surrounded the foot of the hill on which the cathedral stands, it was abandoned by the bishops. At the beginning of the 16th century the humanist Agostino Giustiniani, bishop of Nebbio, had the cathedral repaired. It was also at this time that the belltower was almost certainly added which was destroyed by the 19th century restorers. Despite these works the cathedral was abandoned again in 1576. It was described as being roofless during a visitation by Mgr Sauli, the then Bishop of Aleria.