Kastell Miltenberg-Altstadt, Roman fortification site near Main River in Miltenberg, Germany.

Kastell Miltenberg-Altstadt is a Roman cohort fort in the Altstat field, now called In der Altstadt, about two kilometres northwest of Miltenberg's medieval centre. Its praetorial front faced the Main floodplain, and the medieval Altstadtweg still enters the grounds at the site of the Porta principalis dextra. The fort survives as a raised earthwork, with its wall foundations lying beneath a later medieval wall.

The fort was built in the middle of the 2nd century as part of Rome's frontier defense system in the region. It was abandoned when Roman forces withdrew from the area during the later Roman period.

The field name "In der Altstadt" refers to the medieval settlement of Wallhausen, which later became deserted and whose name likely recalled the walls of the Roman garrison. The modern street Altstadtweg enters the fort site exactly where the Porta principalis dextra, the south-east gate, once stood.

The fort lies in the open field "In der Altstadt", about two kilometres northwest of Miltenberg's medieval centre; the Altstadtweg enters the grounds where the south-east gate once stood. Information boards stand at the left gate, at the right gate's site and at the bath. A railway line cuts through the rear camp, and the foundations lie mostly under farmland.

The fort's ground plan survives as a low rise in farmland, and the Altstadtweg still enters the site exactly where the Porta principalis dextra, the south-east gate, once stood. The military bath lay only a few metres south-east of the fort, and a civilian settlement (vicus) is proven though invisible above ground.