The caponier by the Old Lubelska Gate is the only facility of this type to have been preserved in a good state. It was built in 1836 and its stone and brick elevations match the other fortification facilities of the time. It is a small, pentagonal building situated at the bottom of the moat, above a ditch with water. Inside there were locks, which regulated the level of water. However, the main purpose of the caponier was to protect the moat. Two canon embrasures in the eastern wall and two in the western wall made it possible for soldiers to shoot along the moat, whereas the embrasures for handguns - to shoot at the enemy in front of the fortress. Next to the south-eastern corner of the building a fragment of Carnot wall was reconstructed in 2009.
