The "Kaleto" fortress in Vidin is a medieval fortification built in order to protect the border town, its garrison and the castle of Vidin"s ruler. It was designed by Gezar Mustafa – a Hungarian or Austrian engineer who converted to Islam. The construction of the fortress began during one of the Austro-Turkish wars (1690-1720) by French and Polish builders who were working for Turkey. It was finally completed (without the outer wall) in 1735. "Kaleto" has a total defended area of 7 km² including an Outer town (Varosh) and an Inner city (around 1.5 km²) with the "Baba Vida" fortress and governing and residential buildings for the nobility and the garrison. The Inner city was surrounded by a fortress wall with a ditch, and the Outer – by a ground wall and a ditch, completed around 1838. The 3 defensive circles of "Kaleto" were gradually constructed and strengthened. The Inner circle is "Baba Vida", situated on the Danube river bank – fenced by a moat. The Middle circle is 500-1000 m away from the Inner one and from the landside it forms a semicircle with a diameter of around 1800 m. It has a double stone wall along the riverbank and a single arc-shaped wall on the land around the town. Both walls have fortified gates and defensive bastions 200-250 m away from each other. In front of the walls on the landside there's an outer ditch that's 18 m wide and 5-6 m deep and fills with water from the river. The Outer circle (Reduta) is 1 km away from the Middle one and has a ground wall with fortifications. Similarly to the fortress walls, from the outside it's fenced by a ditch. Today "Kaleto" is partially preserved. From the landside the ditch has been filled up and only 4 of the fortress gates have been conserved: Florentin kapiya, Enicher kapiya, Pazar kapiya and Stambol kapiya – the main entrance gate that leads to Istanbul. You can go to the Danube river through 5 partially preserved gates – Aralak kapiya, Top kapiya, Saray kapiya, Telegraph kapiya and Suyrguyn kapiya. The entire fortress is by its nature a great construction achievement for the time. "Kaleto" was unsuccessfully besieged during the Russo-Turkish Liberation War (1877-1878), the Serbo-Bulgarian War (1885) and for the last time – during the Second Balkan War (1912-1913). The "Kaleto" fortress has been declared an Architectural and Construction Monument of National importance.