Priscillianism is a Christian doctrine developed in the Iberian Peninsula (the Roman Hispania) in the 4th century by Priscillian, derived from the Gnostic-Manichaean doctrines taught by Marcus, an Egyptian from Memphis, and later considered a heresy by the both the Eastern Orthodox Church and the Roman Catholic Church.
Priscillian was described as "a man of noble birth, of great riches, bold, restless, eloquent, learned through much reading, very ready at debate and discussion" (Sulpicius Severus, "Histor. Sac.", II, 46). His first followers were a lady named Agape and a rhetorician named Helpidius. Through his oratorical gifts and reputation for extreme asceticism he attracted a large following, including two bishops named Instantius and Salvianus. The new sect became an oath-bound society, attracting the attention of the bishop Hyginus of Cordoba. Hyginus made his fears known to Hydatius, Bishop of Emerita (Mérida), and Ithacius of Ossonoba. The bishops of Hispania and Aquitaine then held a synod at Zaragoza in 380. Though summoned, the Priscillianists refused to appear, and the synod pronounced sentence of excommunication against the four leaders, Instantius, Salvianus, Helpidius and Priscillian.
Ithacius was chosen to enforce the synod's decrees, but he failed to bring the heretics to terms. In defiance Priscillian was ordained to the priesthood and appointed Bishop of Avila. Ithacius then appealed to the imperial authorities. The Emperor Gratian issued a decree which deprived the Priscillianists of their churches and sentenced them to exile. Instantius, Salvianus and Priscillian proceeded to Rome to gain the aid of Pope Damasus I (also from Iberia) in having this sentence revoked. Denied an audience, they went to Milan to make a similar request of St Ambrose, but with the same result. They then resorted to intrigue and bribery at the Court with such success that they were not only freed from the sentence of exile, but permitted to regain possession of their churches in Hispania, where, under the patronage of the imperial officials, they enjoyed such power as to compel Ithacius to leave the country. He, in turn, appealed to Gratian, but before anything had been accomplished the emperor was murdered in Lyon, and Magnus Maximus had taken his place. Maximus, wishing to curry favour with the orthodox bishops and to replenish his treasury through confiscations, gave orders for a synod, which was held in Bordeaux in 384. Instantius was first tried and condemned to deposition. Thereupon Priscillian appealed to the emperor at Trier. Ithacius acted as his accuser and was so vehement in his denunciations that St Martin of Tours, who was then in Trier, intervened, and, after expressing his disapproval of bringing an ecclesiastical case before a civil tribunal, obtained from the emperor a promise not to carry his condemnation to the extent of shedding blood.
After St Martin had left the city, the emperor appointed the Prefect Evodius as judge. He found Priscillian and some others guilty of the crime of magic. This decision was reported to the emperor, who killed Priscillian and several of his followers; the property of others was confiscated and they were banished. The conduct of Ithacius immediately met with the severest reprobation. St Martin, hearing what had taken place, returned to Trier and compelled the emperor to rescind an order to the military tribunes, already on their way to Iberia to extirpate the heresy. There is no ground in the condemnation and death of Priscillian for the charge made against the Church of having invoked the civil authority to punish heretics. The pope censured not only the actions of Ithacius but also that of the emperor. St Ambrose was equally stern in his denunciation of the case and some of the Gallican bishops, who were in Trier under the leadership of Theognistus, broke off communion with Ithacius, who was subsequently deposed from his see by a synod of Hispanic bishops, and his friend and abettor Hydatius, was compelled to resign.
After the death of Priscillian and his followers, however, the numbers and zeal of the heretics only increased. In 400 another synod was held in Toledo to deal with this problem; many, including bishops Symphonius and Dictinnius were there reconciled to the Church. Dictinnius was the author of a book "Libra" (Scales), a moral treatise from the Priscillianist viewpoint. The upheaval in the Iberian Peninsula due to the invasion of the Vandals, the Alans and the Suevi aided the spread of Priscillianism. Paulus Orosius, a Gallaecian priest from northwest Hispania, wrote to St Augustine (415) to enlist his aid in combating the heresy. Pope Leo I at a later date took active steps for its repression and at his urgent insistence councils were held in 446 and 447 at Astorga, Toledo, and Braga. In spite of these efforts the sect continued to spread during the fifth century. In the following century it began to decline, and after the First Council of Braga (563), which specifically targeted its doctrines, it soon died out.
The foundation of the doctrines of the Priscillianists was Gnostic-Manichaean dualism, a belief in the existence of two kingdoms, one of Light and one of Darkness. Angels and the souls of men were said to be severed from the substance of the Deity. Human souls were intended to conquer the Kingdom of Darkness, but fell and were imprisoned in material bodies. Thus both kingdoms were represented in man, and hence a conflict symbolized on the side of Light by the Twelve Patriarchs, heavenly spirits, who corresponded to certain of man's powers, and on the side of Darkness by the Signs of the Zodiac, the symbols of matter and the lower kingdom. The salvation of man consists in liberation from the domination of matter. The twelve heavenly spirits having failed to accomplish their release, the Saviour came in a heavenly body which appeared to be like that of other men, and through His doctrine and His apparent death released the souls of the men from the influence of earthly matter.
These doctrines could be harmonized with the teaching of Scripture only by a complex system of exegesis, rejecting conventional interpretations and relying on personal inspiration. The Priscillians respected most of the Old Testament but rejected the creation story. Several of the apocryphal Scriptures were acknowledged to be genuine and inspired. Because the Priscillians believe that matter and nature were evil, they became ascetics and fasted on Sundays and Christmas Day. Because their doctrines were esoteric and exoteric, and because it was believed that men in general could not understand the higher paths, the Priscillianists, or at least those of them who were enlightened, were permitted to tell lies for the sake of a holy end. Augustine wrote a famous work, "Contra Mendacium" ("Against Lying") in reaction to this doctrine.
Writings and rediscovery 
Some writings by Priscillian were accounted orthodox and were not burned. For instance he divided the Pauline epistles (including the Epistle to the Hebrews) into a series of texts on their theological points and wrote an introduction to each section. These "canons" survived in a form edited by Peregrinus. They contain a strong call to a life of personal piety and asceticism, including celibacy and abstinence from meat and wine. The charismatic gifts of all believers are equally affirmed. Study of scripture is urged. Priscillian placed considerable weight on the deuterocanonical books of the Bible, not as being inspired but as helpful in discerning truth and error; however several of the books were considered to be genuine and inspired.
It was long thought that all the writings of the "heretic" himself had perished, but in 1885, Georg Schepss discovered at the University of Würzburg eleven genuine tracts, published in the Vienna Corpus 1886. Though they bear Priscillian's name, four describing Priscillian's trial appear to have been written by a close follower.
See also 
- McKenna, Stephen, "Priscillianism and Pagan Survivals in Spain" in Paganism and Pagan Survivals in Spain up to the Fall of the Visigothic Kingdom on-line The present account depends on this thoroughly cited chapter.
- Saunders, Tracy, "Pilgrimage to Heresy", (iUniverse 2007) a fictionalised version. In Spanish as Peregrinos de la Herejía, (Editorial Bóveda 2009)
- Henry Chadwick's landmark book Priscillian of Avila: The Occult and the Charismatic in the Early Church, (Oxford University Press, 1975)
- "Liber Apologeticus" .
- Fletcher, Richard A., "St. James' Catapult: The Life and Times of Diego Gelmirez", Chapter 1 and passim: *Galicia, online at  a historical and geographical background to the building of the cathedral in Compostela
- Burras, Virginia, "The Making of a Heretic", (U. of California Press, 1995)