 The cathedral was severely damaged and pillaged after the siege of Tortona by Frederick Barbarossa in 1155, and again in 1163.The plight of Tortona was made greater due to the firm support of Bishop Oberto for the legitimate Pope Alexander III rather than the Emperor's antipope Victor IV.In 1236 Bishop Petrus Busetto (1221–1255) compiled a set of Statutes for the Cathedral Chapter.