146 MEDLEYAL CIVILIZATION induced their masters to fix their rents, and to release them from the "mortmain/* This was called to en- franchise or simply "abonner" (to fix the limit), This favor was dearly bought, the master granted it only in exchange for large sums, but it was irrevocable. The serf (abonne') henceforth paid a fixed tax only, he and his descendants became in perpetuity free villeins. Therefore, according1 as new villages ob- tained charters, the number of serfs diminished. In the fourteenth century there were no longer any of them to be found in certain provinces; in others (Bur- gundy, Comte, Auvergne) there were a few until the eighteenth century, but only a small number remained. Even those who had not been enfranchised by their master had become more free, the usage was estab- lished that a serf could leave his village on condition of disavowing his master, by declaration made to him, that he no longer recognized him as master; the lord kept the land, but he was obliged to let the man depart.