Castra Mediana, Roman archaeological fort in Gnotzheim, Germany

Castra Mediana is a Roman fort site in Gnotzheim, Bavaria, measuring 159.0 by 144.1 metres (2.3 hectares). Its 1.30-metre-thick wall had four rounded corners with towers. The site lies under farmland on a ridge spur above the Wurmbach; geophysical survey in 2008 mapped its buried plan.

Mediana began under Domitian (81–96 AD) as a wood-and-earth enclosure, one of the oldest forts on the Limes. A building inscription dates the stone rebuild of the 159.0 × 144.1 m (2.3 ha) site to 144 AD under Antoninus Pius, carried out by the Cohors III Thracum. A second inscription from Caracalla's reign (211–217) records a late refurbishment.

Archaeological excavations have uncovered inscriptions detailing the presence of the Cohors III Thracum civium Romanorum equitata, a part-mounted Roman military unit.

The site is accessible by way of field paths and reveals itself mainly through gentle ground rises across the landscape. Walking through the surrounding fields helps visitors trace the subtle soil mounds that mark where buildings once stood.

The best-preserved building inscription from Mediana, recording construction work in 144 AD under Antoninus Pius by the Cohors III Thracum, is set into the south outer wall of Gnotzheim's baroque St. Michael's church. A second, fragmentary inscription from Caracalla's reign (211–217) is visible inside the church on the south side.