ベルトラン・デュ・ゲクラン
Having acquired the lordship of Josselin, Olivier began to build Josselin Castle in 1370, an imposing new fortress with eight towers. In the same year, he joined [[Bertrand du Guesclin], the [[constable of France]], and followed him in campaigns against the English, including the Siege of [[Brest, France|Brest]] in 1373.