Kastorbrunnen, Water well in front of St. Kastor Basilica, Koblenz, Germany.

Kastorbrunnen is a large rectangular block of Niedermendig basalt with a high, chamfered base and a projecting top slab, standing in front of St. Kastor Basilica in Koblenz. Two semicircular basins of Lahn marble hang on its sides. It was designed by military engineer Dagobert Chauchet and carved by the Aachen sculptor Rauch.

Built in 1812 by French prefect Jules Doazan to commemorate Napoleon's Russian campaign, the well later received a response carved by a Russian commander. The twin inscriptions now mark this moment when military fortunes changed dramatically.

Two inscriptions in French appear on the fountain, one from French forces and another from a Russian commander, reflecting a moment when opposing armies met at this spot. The texts remain visible today, serving as a conversation frozen in stone.

The well is located in central Koblenz near St. Kastor Basilica and remains accessible throughout the day without restrictions. It works best to visit as part of exploring the surrounding plaza and the old town area nearby.

A Russian commander responded to the original inscription with text of his own, creating an unusual dialogue between enemies on stone. This rare moment of wit during wartime remains frozen in the inscriptions for visitors to read today.