Marcian (Marciano, Marziano, Marcianus) of Tortona (died 117 or 120 AD) is a saint of Roman Catholic church.

He is traditionally said to have been the first bishop of Tortona, in what is now north-western Italy, a post he held for forty-five years.

Tradition states that he was born to a pagan family but was converted by Barnabas and then confirmed in the Christian faith by Sirus (Siro), bishop of Pavia.

Secundus of Asti is said to have met Marcian at Tortona, when the former was still a pagan.

Walafrid Strabo, in response to the construction of a church in honor of the saint, indicates that Marcian was the first bishop of the Tortonese community and a martyr.