ENFortified churches are the most distinctive phenomenon of the sacred architecture of the Grand Duchy of Lithuania. The question of the origin of the form of fortified church with four corner towers was addressed by many Belarusian and foreign researchers. M. Tkachou and T. Habrus considered that the prototype of this form was the cathedral of St.Sophia in Polack, rebuilt at the end of XV - beginning of XVI century; M. Shchakacihin proposed the Bernardine church in Vilnius; A. Kushniarevich proposed the cathedral of St. Stanislaus in Vilnius, in fact, most of fortified churches combine western gothic tradition (fortification elements, building structures} with eastern Old Russian principles of interior planning. In our opinion, the development of the type of fortified churches was influenced by the tradition of the so-called towers of Volhynian type, which came to the Grand Duchy of Lithuania from Volhynia at the end of XIII century. A tower of Volynian type is the central element of a castle, fit for isolated defence. They originate from the tradition of French donjons and German bergfrieds. Erection of such towers became quite widespread in the Grand Duchy in XIII century, and this tradition remained influential further. In particular, the type of Teutonic castles was alterated, and some of them (Medininkai, Kreva) got mighty corner towers.An the end of XIV - beginning of XV century building of mighty fortification towers ceases. This was motivated by the development of the art of fortification, as welf as by the growing demand for comfort among nobles. The function of the symbol of feudal power was inhereted by castellated pataces. in particular, the palace of Vitaut on the Upper castle of Vilnius had fortification towers on the corners, and probably became a prototype for the fortified churches with four corner towers. In this way, a type of separate building designed for isolated defence evolved from Volhynian - type towers into fortified churches.