 It was built in 1028 by the Compte de Cornouaiile.Alain Canhiart was buried in the chapel in 1058, following a vow made by Canhiart that his armies would be successful in the battle of Locronan.When in 1239, Monseigneur Raynaud planned the construction of the choir of the new cathedral, the decision was made to add the old chapel to the choir, this being one of the reasons for the odd shape of the cathedral with the choir leaning slightly to the left of the transept.