Dedicated to Saint Samson of Dol (died ca. 565). It was formerly the seat of the Archbishop of Dol, one of the nine ancient bishoprics of Brittany. The archbishopric was suppressed during the French Revolution and abolished by the Concordat of 1801, when it was merged into the dioceses of Rennes and St. Brieuc. The incomplete north tower on the main west-facing entrance was begun in 1520 but never finished due to lack of funds.