JAN VAN RUUSBROEC (1293–1381) was introduced to the Middle English readership of The Treatise of Perfection of the Sons of God as ‘dan john rusbroke, the first prior of the chartyrhowse in valle viridi iuxta bruxellam’. The anonymous translator of De calculo candido, the Latin translation of Ruusbroec's Vanden blinckenden steen (The Sparkling Stone) was right about both Ruusbroec's function and location, but mistakenly presented him as a Carthusian.

Ruusbroec was the prior of the monastery of Augustinian canons regular at Groenendaal, not far from Brussels. He was one of a community of five men, three priests and two laybrothers, who in 1434 were given permission by Duke Jan III of Brabant to start a religious community in an abandoned hermitage in the forest of Soignes. While still at Brussels, the three priests – Vranke van den Coudenberg, Jan Hinckaert, the chaplain who had been responsible for his kinsman Ruusbroec's upbringing, and Ruusbroec – had already given up the worldly life of the clergy associated with the wealthy cathedral chapter in favour of an apostolic life of poverty and contemplation. The move to Groenendaal added the physical solitude of the forest to the spiritual solitude the men had chosen and lived amid the hustle and bustle of the Cathedral town. The community soon adopted the rule of St Augustine and became a monastery of Augustinian canons. It grew and prospered, with the astute organizer Vranke van den Coudenberg as dean, and Ruusbroec as prior.