A reissue of Sir Steven Runciman's classic account of the Dualist heretic tradition in Christianity from its Gnostic origins, through Armenia, Byzantium, and the Balkans to its final flowering in Italy and Southern France. The chief danger that early Christianity had to face came from the heretical Dualist sect founded in the mid-third century AD by the prophet Mani. Within a century of his death Manichaean churches were established from western Mediterranean lands to eastern Turkestan. Though Manichaeism failed in the end to supplant orthodox Christianity, the Church had been badly frightened; and henceforth it gave the hated epithet of 'Manichaean' to the churches of Dualist doctrines that survived into the late Middle Ages.