Burgruine Altenburg, Medieval castle ruin in Felsberg, Germany

Burgruine Altenburg is a medieval castle ruin perched on a basalt hilltop near Felsberg, overlooking the Eder River valley below. The site features a tall keep and substantial wall sections that showcase the scale of this former fortification.

The Altenburg was probably the first residence of the Amtgrafen von Felsberg, first mentioned in 1060, before they moved to the nearby Felsburg from 1072/1090 to 1286. It was first documented as Aldinburg in 1322, when the widow of Werner von Besse and her heirs exchanged it with a watermill and fishing rights to Landgrave Otto I of Hesse for four hides of land before the town of Felsberg. Landgrave Heinrich II renewed it in 1333, and the brothers Hermann and Gottschalk von Holzheim built the mantlet wall and the surviving keep between 1388 and 1392. In 1525 a Franconian peasant troop took and burned it during the Peasants' War.

The name Altenburg ("old castle") distinguishes it from the Felsburg, the "rock castle" built later about 2 km northeast. From 1428 the Holzheim, Elben, Linne and Gilsa families held shares as Burgmannen, and in 1489 Thiemo von Wildungen received a castle seat. The Boyneburg family, who acquired the ruin in 1537, built the Herrenhaus at the foot of the hill in 1721.

The ruin stands on a basalt knoll on the left bank of the Eder, directly opposite the mouth of the Schwalm, about 2 km southwest of the Felsburg. The keep, sections of the ring wall, remains of the residential wing and two barrel-vaulted cellars beside the entrance are preserved; the site is to be restored.

The keep that still stands was built between 1388 and 1392 by the brothers Hermann and Gottschalk von Holzheim, who held half the castle as a pledge fief from Landgrave Heinrich II. They also raised the Mantelmauer, the shield wall protecting the upper ward. The slender tower with parts of its battlement ring is their work.