The gnostics also believed something radically different from what today we would call traditional Christianity. The essential doctrine which set the gnostics apart was a belief that there was a good God and an evil, insane creator god, the god who created the earth being the evil one. This caused some rather radical theories about Jesus, such as, Jesus being the true Son of the good God was sent here to release us from the bondage of the insane creator god, Samael and therefore, not being a creation of Samael, Jesus could not have taken on flesh and therefore could not have died on the cross.
Furthermore, true salvation came from gnosis, or direct knowledge imparted by the True God and not from a church hierarchy and definitely not from the crucifixion for the reason stated above.
During the 12th and 13th century there was a resurgence of gnosticism starting with the Bogomils of the east influencing the Cathar movement in Occetania (today southern France) and led to the Albigensian crusade. The society of the Cathars was one of believers and the Perfected. When a believer was near death, a Perfecti was summoned who would impart a ritual to the dying believer that was supposed help them in the next life remember who they were and the true nature of the world and this ritual was supposed to shorten the length of time it took to be freed from Samael's false creation and united with the True God above the false creator God of this world. Can't quite remember how this final transition was supposed to happen.
After the Albigensian Crusade, the Bogomils continued for a time in the east but finally the western church pressured the eastern church and they were somehow wiped out also.
Afterward, the gnostics disappear from history and not much thought of until the discovery of the Nag Hammadi Codex in, was it 1944? So either they were all wiped out by the 14th century or learned to keep very, very quiet.