Basilica of St. Castor, Romanesque parish church in Koblenz, Germany

The Basilica of St. Castor is a Romanesque church near the Deutsches Eck in Koblenz. Its west front has two tall towers with steep pointed roofs and a clock on the right tower; the main entrance sits between them under a small gable. Inside, a nave with round-arched arcades on grey stone columns leads to a raised altar and a curved apse.

The original building was constructed in the early 800s under Archbishop Hetto of Trier with support from Emperor Louis the Pious. The structure was modified several times over the centuries and now shows features from different periods.

The church is dedicated to Saint Castor, a 4th-century missionary on the Moselle who founded a religious community at Karden; his relics were brought here for the 836 consecration. Rizza, said to be a daughter of Louis the Pious, is venerated as a saint of Koblenz, and her shrine still stands in the church.

The church stands just behind the Deutsches Eck on the spit between the Rhine and Moselle, a short walk from the old town. The main entrance lies between the two west towers, and the Kastorbrunnen fountain sits on the forecourt. The nave is entered from the west end, with the raised choir and apse at the far east end.

The Kastorbrunnen in front of the basilica was built in 1812 during Napoleon's Russian campaign. Its inscriptions, carved by French soldiers, were later supplemented with Russian text after the Russians reached Koblenz, so the fountain records both sides of the conflict.