Koblenz Fortress, Military fortress in Koblenz, Germany.

Koblenz Fortress is a Prussian fortress system of six sections built from 1815 onward, with ramparts, forts and batteries around Koblenz and Ehrenbreitstein. Its main work, the Ehrenbreitstein citadel, stands on a height above the Rhine and Moselle confluence. The photograph shows grey-brown masonry laid out in angular, star-shaped ramparts, a long walled approach, a pale flat courtyard with low dark-roofed buildings, and massive sloped bastions stepping down in tiers, their tops edged with grass and scrub.

Koblenz Fortress was built by Prussia in three stages: 1815–1830, 1859–1868 and 1871–1886, designed by Ernst von Aster and Gustav von Rauch. King Frederick William III issued the order for its construction on 11 March 1815, after the Congress of Vienna gave the Rhineland to Prussia. The citadel replaced the Electoral Trier fortress on the Ehrenbreitstein, blown up in 1801. Parts were declassified in 1890, the gates demolished between 1896 and 1899, and more structures removed in 1920–1927.

The name of the Ehrenbreitstein citadel comes from the medieval castle of Ehrenbert, replaced in the 19th century by the Prussian fortress. The main work of each of the six sections was called a "Feste"; the term "System" for these sections came into use from 1865. The fortress is classed as classicist, though works on the left bank of the Rhine borrow forms from medieval and Renaissance architecture.

The best way to reach this location is by cable car from the Rhine embankment, which provides views of the river and surrounding landscape during the journey. The grounds are spacious and comfortable walking shoes are advisable for exploring.

At its completion the fortress was considered impregnable, like Gibraltar, and its 14 km of works matched the scale of Paris and Cologne. It was the first example of the 19th-century Großfestung type, built in the Neupreußische Befestigungsmanier with a polygonal system instead of bastions.