Château de Sully-sur-Loire, Medieval castle in Sully-sur-Loire, France

Château de Sully-sur-Loire stands on the left bank of the Loire at its confluence with the Sange, in Sully-sur-Loire, Loiret. It has two parts: the rectangular keep, flanked by four round towers and entered from the south through a gate flanked by two towers, and the Petit Château closing the courtyard to the south. The keep's attic holds a 14th-century pointed barrel-vault roof frame; the moats are still water-filled.

A castrum is documented here in 1102, controlling a ford over the Loire. In 1218 Philip Augustus seized the lordship and built a cylindrical keep in the outer courtyard; from 1395 Guy de La Trémoille and Marie de Sully raised the present keep, finished by Marie after his death in 1396. Maximilien de Béthune bought the barony in 1602, made it a duchy-peerage in 1606 and remodelled the interior.

The castle hosts the Festival de Sully et du Loiret, an international classical and contemporary music festival held each May and June since 1973. Inside the keep, the first-floor great hall keeps its 17th-century wooden doors and a painting of the Château de Rosny-sur-Seine above the fireplace. A wrought-iron door there opens onto Maximilien de Béthune's small study, known as the cabinet de Sully.

The castle stands on the left bank of the Loire, next to the bridge and at the corner of the chemin de la Salle verte and the promenade des douves. The moat around it is fed by the Sange. The park is bordered by canals that Maximilien de Béthune had dug to protect the site from Loire floods.

The keep's attic holds a 14th-century timber roof frame built as a pointed barrel vault, a carpentry work from the campaign of Guy de La Trémoille. The two western towers of the keep were left unfinished and empty when Marie de Sully completed the building after her husband died at Nicopolis in 1396.