The mystic treatises of Jan Ruysbroeck (1292-1381), who may be considered as the founder of Flemish prose, just as van Maerlant is the founder of Flemish poetry, are far more important than the rhymed chronicles of Boendaele. Not only do they rank among the most inspired religious writings of the Middle Ages, but they are the expression of a deep-rooted religious movement which animated the Flemish bourgeoisie at the time, and which had its origin in the foundation of the institution of the Beguines and the Beggards, so active and so influential during the twelfth century. This movement aimed at bringing religion closer to the common people through the work of laymen who, though deeply attached to the Church, were conscious of its limitations and of the barrier which aristocracy and privilege had built around it. One of Ruysbroeck's disciples, Gerard de Groote (1340-84), founded the Order of the "Freres de la Vie Commune" (Brothers of the Common Life), and the "Sustershuysen," which contributed so much to the revival of religious studies and general education in the early days of the fifteenth century. Like the Beggards, the Brothers did not strictly constitute a religious order, they did not pronounce any binding vow and retained their lay character. Refusing any gift or endowment from outside, they had to provide for their own needs, but, while the Beggards devoted most of their time to the weaving industry, the Brothers gave themselves up to copying manuscripts, learning and teaching. Under Florent Radewyn, one of de Groote's early disciples, they acquired a very complete organization and founded numerous schools, specially in Brussels (1422) and in Ghent (1432), their influence spreading as far as Germany. Thierry Maertens, the first well-known Belgian printer, was one of their pupils. This educational and religious revival is closely connected with the foundation of the University of Louvain in 1426. De Groote and his disciples were frequently attacked, chiefly by the monks, who became jealous of their success, but their strict orthodoxy and the unimpeachable character of their life made their position unassailable. De Groote was equally well known for his criticism of the abuses among the clergy, his denunciation of the luxury displayed by the rich and the mystic character of his preaching. He was equally severe against heretics, and was called by his contemporaries "malleus hereticorum." Another of his followers founded the celebrated monastery of Windesheim, where, half a century later, the _Imitation of Christ_ was written.