Castellum of Weltenburg-Frauenberg, Roman fort archaeological site in Kelheim, Germany

The Castellum of Weltenburg-Frauenberg is a Roman fort that sits on a rocky spur overlooking the Danube River. The site occupies a strategically important location where the water served as a natural boundary and defensive structures were built for protection.

The site was built during Roman times as part of the Donau-Iller-Rhein-Limes, a major fortification system marking the empire's northern frontier. Later, the location may have served as a bishop's seat during the early medieval period.

The site takes its name from the nearby Frauenberg, crowned by a church that shapes the local landscape. The area became linked to religious life as it later developed into a center of monastic activity in the region.

The remains lie on a rock spur on the Frauenberg above the Danube, at the entrance to the Danube gorge near Weltenburg. The slope falls steeply to the river, so the site is reached on foot and the marked paths should be kept to. As a protected archaeological monument, any excavation requires prior permission from the Bavarian authorities.

The site was long known as the Römerwall, and Johannes Aventinus recorded a legend that Saint Rupert of Salzburg built a chapel over a temple of Minerva here. The present church on the spot is a Baroque building erected under Abbot Maurus I. Bächl (1713–1743).