an heretic, born at Sinope in Paphlagonia, or Pontus, in the second century. In his younger years he followed the stoic philosophy, and loved solitude and poverty; but being convicted of uncleanness with a virgin, he was expelled the church by his father, who was bishop. Afterwards he came to Rome, where he invented his heresies. His doctrines were, many of them, the same that were afterwards adopted by the Manichaeans; as, for instance, that there two coeternal independent principles, one the author of all good, the other the author of all evil. Marcius meeting St Polycarpus in the streets of Rome, asked him, whether he knew him? "Very well," answered the bishop, "I know you to be the devil's eldest son." Tertullian relates, that Marcius, repeating of his errors, would have abjured them publicly, provided he might have been again admitted into the church; which was agreed to, on condition he would bring back all those he had seduced from it; but before he could effect this task, he died.