 The original cathedral was said to have been founded on the citadel of Tortona in the second half of the 4th century by Bishop Innocentius.It was dedicated to S. Sixtus and S. Lawrence, though the name of Sixtus was subsequently omitted, and that of Innocentius added.In 945 or 946 Bishop Giseprando (943–after 963) added the name of S. Martianus to the list of patrons of the cathedral.