Castra Ad Iuvense, Roman military fort in Wallsee-Sindelburg, Austria.

Castra Ad Iuvense is a Roman military fort in Wallsee-Sindelburg situated on an elevated rocky plateau overlooking the Danube valley. The fortified settlement featured a rectangular layout with barracks, storage buildings, and administrative structures typical of Roman military installations of this era.

The fort was founded in the 1st century as a timber-earth fortification and later rebuilt in stone to better defend the Roman Empire's frontier along the Danube. The site remained occupied for several centuries and underwent various modifications until its decline in the 5th century.

This fort was where Roman soldiers and local river communities came into contact and exchanged goods and ideas. The everyday objects found here reveal how military life blended with the customs of people living along the Danube's shores.

The fort lies beneath the Wallsee town centre, so there is no open excavation to walk through; the surviving late antique corner fort in the southeast was conserved until 2018 and opened to visitors inside a new building. The site sits on a rock plateau above the Danube, reached on foot through the village.

The fort's identification with Ad Iuvense is debated; a brick stamp found at Wallsee and St. Marienkirchen am Inn names the site Loco Felicis, Latin for 'the fortunate place'. The late-antique remnant fort in the southeast corner is among the best preserved small fortresses on the upper Danube Limes, comparable to Zeiselmauer, Traismauer and Rusovce.