A fire broke out on Tuesday in the Saint-Alain cathedral in Lavaur, Tarn.
The fire started in one of the side chapels.
According to preliminary evidence, it could be arson.
An employee of the parish discovered the fire. At around 6 pm, she approached the cathedral and could smell smoke. She reported the incident, and firefighters arrived at speed.
Police said the fire started on a wooden alter, and they are investigating the theory that the fire was started deliberately.