Vidin Fortress, Medieval fortress in Vidin, Bulgaria.

Vidin Fortress, known as Kaleto, is a medieval city fortress with three defensive rings. The inner ring is the Baba Vida citadel on the Danube bank, surrounded by a water-filled moat. The middle ring lies 500–1,000 m inland and includes stone walls, 13 gates, and an 18 m wide, 5–6 m deep moat. The outer ring is an earthen rampart with redoubts.

The fortress grew from the ruins of Roman castell Bononia that had occupied this site since ancient times. Tsar Ivan Stratsimir expanded and reinforced it in the 14th century, creating the structure visible today.

The name Kaleto is a Bulgarian adaptation of the Turkish word for fortress; the Ottomans also called it the Virgin Fortress because it was never taken by force. The main gate by the central square is the Stambol Kapia, and the river gate near Baba Vida is the Top Kapia.

The site sits directly on the riverbank and is easily reached from the city center. Wear sturdy shoes since pathways cross uneven ground and include stairs throughout the grounds.

Ottoman sources called it the Virgin Fortress because it was never taken by force. It withstood the Romanian siege of January 1878 and was handed over only after a sultan's order following the Edirne armistice.