Altenburg, Prehistoric hilltop fortification in the Spessart, Bavaria, Germany

Altenburg is a prehistoric hilltop fortification on the Schlossberg between Soden and Ebersbach in the Spessart. It measures 365 meters east-west and 180 meters north-south, and a double ring wall still surrounds the summit plateau. The inner wall's collapsed remains suggest a post-slot wall, and a reconstructed post-slot wall and Celtic house now stand on the site.

The Altenburg is a prehistoric hilltop enclosure, not a medieval castle. Excavations in 2008 and 2009 by the Archäologische Spessartprojekt identified a Michelsberg Culture phase (about 4400–3500 BC) and a Celtic fortification of roughly 600–450 BC. Charred oak beams in the inner rampart gave a felling date no earlier than 613 BC, with radiocarbon results pointing to about 450 BC.

The site is linked to the legend of the "Aleborgfraale", a figure said to guard a treasure that can only be found at night before St John's Day by someone who stays silent during the search. Since the excavations, the Sulzbach and Leidersbach history societies have rebuilt a post-slot wall and a "Celtic house" on the grounds, with information boards for visitors.

The site is accessible via marked hiking trails from nearby parking areas with informational panels on-site. Visitors should expect uneven ground and some steep sections along the route.

Excavations on the site uncovered multiple construction phases from different time periods. These findings reveal how the complex was reshaped and adapted to changing needs across generations.