ENBased on the written sources and the results of archaeological excavations, the article examines the initial appearance of Viciebsk masonry castles in the fourteenth century and their transformation in the period up to the middle of the seventeenth century. The powerful complex of masonry fortifications was built in Viciebsk in the fourteenth century. It included the Upper and Lower Castles and occupied an area of about 11 hectares. Its perimeter was covered by natural obstacles, fortified by men, brick and wooden walls with a total length of about 2 km and at least 10 brick towers. The construction of masonry fortifications was not completed, and 26 % of the defense line of the Upper Castle, as well as 41 % of the fortifications of the Lower Castle, always remained wooden. Over the centuries, Viciebsk castles changed their functions several times. They were built as Alhierd’s residence in one of the main centers of his patrimonial possessions, and in the sixteenth and seventeenth centuries they actually continued to function as a state fortress of the Grand Duchy of Lithuania. The main reasons for the gradual destruction and disappearance of castle fortifications were time and absence of a system of care for their masonry part. The article also examines the social structure of the population of Viciebsk castles and the functioning of services related to providing them with the necessary resources and services. In the fourteenth-seventeenth centuries, the castles were densely populated.In addition to the residence of the monarch and his local government official, real estate belonging to the nobility, burghers, church and other categories of owners was located here. The system of building and providing fortifications in the fourteenth–seventeenth centuries gradually evolved from the natural duties of the population of the land to extraordinary measures and attracted additional funding. Keywords: castle, residence, fortress, fortification, Viciebsk, Belarusian Podvine, Grand Duchy of Lithuania.