Burg Sponeck in Sasbach, Medieval castle ruin in Sasbach am Kaiserstuhl, Germany

Burg Sponeck is a castle ruin positioned on a rocky ridge near Sasbach am Kaiserstuhl in Baden-Württemberg, commanding views over the Rhine valley on three sides. The site displays characteristic features of a hilltop fortress with partially preserved walls and a distinctive defensive tower.

The castle was built atop a late Roman fort constructed in the 4th century under Emperor Valentinian I, whose foundations remain visible in the archaeological record. The site later developed into a medieval hilltop fortress that controlled this strategically important Rhine position.

The castle's name comes from the Spenlin family, Burgmannen in Breisach from 1245; Hildenrand Spenlin is documented in 1262, and in 1305 Spanegg appears as the possession of Johann, son of the knight Hildebrand Spenli, imperial Schultheiss of Breisach. The counts of Sponeck, related to the House of Württemberg, took their name from the castle. In the 19th century the Burkheim innkeeper Sebastian Sichler held the ruin as a hereditary fief and ran a tavern inside it.

The ruin stands on a 25-metre rock spur west of Jechtingen. The Rhine once surrounded it on three sides, but Tulla's straightening moved the river about 200 metres west, so the rock is now entirely landlocked. The site is a heritage monument; no opening times or private ownership are recorded in the sources.

The castle was built after 1281, when the peace treaty between King Rudolf and Freiburg obliged the city to pay 800 marks of silver for a new castle; since Spanegg was an imperial fief and no other such castle was built in the Breisgau, this sum is linked to Sponeck. The counts of Sponeck, related to the House of Württemberg, took their name from the ruin.