The cathedral, dedicated to Saint Tugdual, the monk who founded Tréguier, is one of Brittany's most beautiful religious buildings. Built of Caen stone, schist and granite, it began in the Romanesque style in the 11th century and was completed in 1470 under the Gothic influence with the inauguration of the cloister. With its 48 arcades, stone buttresses and wooden vault, the cloister is the most complete surviving in Brittany. The 18th-century spire towers over the town at a height of over 60 metres. Card game motifs adorn this stone sentinel: a reference, it is said, to the lottery finances from which Louis XVI drew to finance it. Inside the cathedral, the tomb of Saint-Yves is remarkable.