The necessity of an additional fortification of Vidin, which after the year 1718 became a border city for the Ottoman empire has made the High Porte to build in Vidin the so-called “Kale” for a period of 30 years (1690 – 1720) – fortress walls which encircle the city in every direction. That fortress system has been preserved up to the present and it is the only Ottoman defense system of such kind in Bulgaria that has been kept to nowadays.