 It continued to develop in the Mediterranean and Middle East before and during the 2nd and 3rd centuries, but decline also set in during the third century, due to a growing aversion from the Catholic Church, and the economic and cultural deterioration of the Roman Empire.Conversion to Islam, and the Albigensian Crusade (1209–1229), greatly reduced the remaining number of Gnostics throughout the Middle Ages, though a few Mandaean communities still exist.Gnostic and pseudo-gnostic ideas became influential in some of the philosophies of various esoteric mystical movements of the 19th and 20th centuries in Europe and North America, including some that explicitly identify themselves as revivals or even continuations of earlier gnostic groups.