Porta Praetoria in Regensburg, Roman gate in Regensburg, Germany.

The Porta Praetoria in Regensburg is the surviving left tower, about 11 metres high, and the right passage of the north gate of the Roman legionary camp Castra Regina, built in the 2nd century AD. A row of five courses of square blocks stands 7 metres to the right, part of the camp wall beyond the lost right tower. The gate originally had two passages flanked by two semicircular projecting towers.

The gate was built around 179 AD under Emperor Marcus Aurelius as the main entrance to the Roman military camp Castra Regina. This fortification protected the Roman military position on the Danube for several centuries.

The gate was already called Porta Aquarum, or Water Gate, in a document of 932, because it led from the eastern old town to the Danube landing and the Stone Bridge. That name faded in the 15th century after the medieval city wall cut off the direct route to the river.

The gate is located in the old town close to the Stone Bridge and Cathedral and is easily reached on foot. Note that wheelchair access is limited and the surrounding area has cobblestone streets.

Only the left tower, about 11 metres high, and the right passage survive; a row of five courses of ashlar blocks stands 7 metres to the right. In 1971 the missing foundation of the right tower was found in the conserved central foundation, proving the gate originally had two passages flanked by two half-round towers.