Marco of San Martino was described as the "companion" of Duke Giuliano during the latter's rocky transition to power in 1492. He was a Giuliano loyalist in the struggle against Count Federico. His exact title was never given.
His support of Guiliano was absolute. He was once chained in the dungeon of San Martino's castle but steadfastly refused to say anything against his friend, even though it could have eased his punishment.
He tended to advise Giuliano to take a more aggressive stance against Federico and his men. He advised that the captured Federico loyalist Rossini be punished severely. Giuliano instead chose to see Rossini dealt with according to sanctioned legal principles.