Castello della Contessa Adelaide, Medieval castle in Susa, Italy

Castello della Contessa Adelaide stands on the height above Susa's historic centre, beside the Arch of Augustus. Its buildings form an L: the shorter east wing, dated to the 10th–11th century, faces the old town and keeps a marble postern and a blocked two-colour bifora; the longer north wing, with an 18th-century appearance, runs toward the Roman arch. The west side retains a carriage gate in a wall with partly demolished towers.

The site was the pre-Roman command area of the Celtic chief Donno and later held the Roman Praetorium, a governor's palace of about 75 by 42 metres beside the Arch of Augustus. In the 11th century the castle passed to the House of Savoy through the marriage of Otto of Savoy to Adelaide of Susa, and he asserted his rights over it in 1051.

The castle is named after Adelaide of Susa (1015–1091), marchioness of Susa and countess of Turin, who in the 11th century brought the old Segusio, the surrounding lands, many Piedmontese fiefs and the Mont Cenis Pass into the orbit of the House of Savoy. Since 2017 its rooms house the city's Museo Civico and a Val di Susa interpretation centre, opened with a lecture by Giuseppe Sergi on Adelaide and a first exhibition, "Abiti, armi e gioielli al tempo di Adelaide".

The fortress sits within easy reach of Susa's town center and is visible from the surrounding hiking trails. Visitors should wear sturdy shoes since the climb to the castle can be steep and the paths are often uneven.

Archaeological work has uncovered that beneath the medieval fortress lie the remains of a much older military installation from pre-Roman times. These layered remains from different periods make this spot a record of how the region's defense strategies evolved over centuries.