Flagellants are practitioners of an extreme form of mortification of their own flesh by whipping it with various instruments.
Flagellantism was a 13th and 14th centuries movement, consisting of radicals in the Catholic Church. It began as a militant pilgrimage and was later condemned by the Catholic Church as heretical. The followers were noted for including public flagellation in their rituals.
Flagellation (from Latin flagellare, to whip) was quite a common practice amongst the more fervently religious. Various religions, like the cult of Isis in Egypt and the Dionysian cult of Greece, practiced their own forms of flagellation. In ancient Rome, eunuch priests of the Phrygian goddess Cybele, the Galli, flogged themselves until they bled during the annual festival called Dies sanguinis (Day of Blood). Women were flogged during the Roman Lupercalia to ensure fertility.
Particularly following the example of the Benedictine monk Peter Damian in the 11th century, flagellation became a form of penance in the Catholic Church and its monastic orders. The 11th-century zealot Dominicus Loricatus repeated the entire Psalter twenty times in one week, accompanying each psalm with a hundred lash-strokes to his back. The distinction of the Flagellants was to take this self-mortification into the cities and other public spaces as a demonstration of piety. As well as flagellation, the rituals were built around processions, hymns, distinct gestures, uniforms, and discipline. It was also said that when singing a hymn and upon reaching the part about the passion of the Christ, one must drop to the ground, no matter how dirty or painful the area may seem. Also one mustn't move if the ground has something on it that may cause an inconvenience.