In the Middle Ages the lands of Belarus were called the «country of castles» because more than a hundred castles, strongholds and other buildings of this type were constructed in this relatively small area. The vast trade routes running across these lands were the reason of constructing so many fortifications there. After several centuries, stone castles were built in the 14th and 15th centuries. They protected the border of the Grand Duchy of Lithuania and were seats of different orders. Despite the fact that few historical buildings managed to survive numerous wars and the collapse of the Soviet Union, the strongholds, which at present are the true Belorussian gems, still remain in these picturesque lands. The buildings of this type include Nesvizh Castle – the legendary residence of the influential Radziwiłł family, Mirsky Castle that has been present in various historical films many times as well as the Old Hrodna Castle, where the sessions of the Sejm of the Polish–Lithuanian Commonwealth were once held.