Aleth Cathedral
Aleth Cathedral () was a Roman Catholic church located in Saint-Servan in Saint-Malo, Brittany, France. It was the cathedral of the diocese of Aleth. Aleth was a Gallo-Roman settlement on a peninsula on one side of the Rance estuary. The diocese was established in the 9th century. The cathedral was destroyed by Norman invaders in the 10th century but later rebuilt. The site of Aleth however was not a secure one and the town of Saint-Malo had begun to grow up on a far more defensible site on a rocky islet in the estuary. In 1146 the seat of the bishopric of Aleth was moved to Saint-Malo by the then bishop, Jean de Châtillon, and established in the monastery, founded in 1108. The diocese thus became the Diocese of Saint-Malo and the abbey church Saint-Malo Cathedral, replacing the cathedral in Aleth. Competition with the new town came to a head in 1255, when resentment in Aleth at the tax demands of Saint-Malo resulted in armed conflict. Aleth lost, and the walls, fortress and church were dismantled as punishment. The former cathedral ruins are still to be seen in the commune of Saint-Servan which occupies the area of the former Aleth. References

Sources
 Organs in France: brief history of cathedral  
 Catholic Hierarchy: Diocese of Saint-Malo 

Former cathedrals in France
Churches in Ille-et-Vilaine
Ruins in Brittany
Monuments historiques of Ille-et-Vilaine
Roman Catholic cathedrals in France