The Albigensians in the south of France during the Middle Ages were gnostics. Gnosticism has survived even to this day, if you count all Christians who believe that they have "special knowledge" that departs from the canonical scriptures. That gnostic vice is the same vice that resulted in Adam's fall. "Eat of this tree and ye shall be as gods!" Orthodox Christianity has never been about special knowledge.
Wow. Speaking of poor grasp ...
The sects of Valentinus and Basilides were extremely popular until the 4th century.
Marcionites plagued the Church well past the 5th century.
In the west, the Manichean school lasted into the 5th century (St. Augustine was a member for 10 years before he accepted the orthodoxy in 382). It was still active in Persia and Tibet until the 17th century.
A resurgence of Manicheanism spawned the Paulicians of Anatolia and the Cathars of France in the 9th century.
It was the suppression of the Cathars (Albigensian Crusade 1147-1229) that led to the creation of the Dominican Order. After the war the Inquisition was established to root out any remaining heretics. Which it infamously did until the last Cathar was executed in 1321.
The Apostle's Creed was the church creed written to ferret out Gnostics, and it was in use by the early 2nd Century.
Marcionites, and late 2nd Century (Confession of St. Irenaeus 180CE).