Archaeologists say Roman Cologne is rising again beneath the modern city after a series of major discoveries during excavations tied to the underground tour of the MiQua – LVR Jewish Museum.
The work, carried out in the Archaeological Quarter of Cologne, reached unusual depths below the town hall square. That depth proved critical. Early embankments along the former Rhine slope had sealed parts of the Roman city during antiquity, protecting structures that would normally have been destroyed by later construction.
Researchers said the conditions created a rare window into Cologne’s Roman past, exposing civic, administrative, and religious remains spanning several centuries.
Massive basilica foundation uncovered
One of the most striking finds is the foundation of an apse from a 4th-century Roman basilica. The structure measures up to four meters thick and formed part of a large, multi-aisled public building. Such basilicas served administrative and civic functions in late Roman cities.
Initial inspection suggested the foundation might be Roman cast concrete, known as opus caementicium. Detailed analysis showed otherwise. Builders used layered tuff, basalt, and limestone. They bonded the stone with a strong mortar made of crushed brick and gravel. The method created a durable base capable of supporting a monumental structure.
Deep excavations beneath Roman Cologne reveal a 4th-century basilica foundation, a rare Roman staircase, and a 2nd-century household altar — all preserved by ancient embankments along the Rhine.#RomanCologne pic.twitter.com/3Lqj4lII42
— Tom Marvolo Riddle (@tom_riddle2025) February 11, 2026
Before excavation, the site appeared only as a shallow depression on the square. Today, the foundation stands exposed and accessible to visitors for the first time.
Early imperial staircase reveals urban planning
Archaeologists also uncovered a staircase dating to the late 1st century. The steps once linked a low-lying area near the Rhine to higher ground connected with the early praetorium, the Roman governor’s palace. The precise endpoint remains unknown.
Staircases rarely survive in Cologne’s archaeology. Later development usually erases upper architectural features. In this case, early backfilling during Roman times shielded the structure from damage.
The discovery offers new insight into how Roman planners adapted the settlement to its sloping riverfront terrain.
Household altar sheds light on daily ritual life
Inside the praetorium complex, researchers identified a 2nd-century household altar. The shrine stood within a wall niche where residents made offerings to the Lares, protective household deities.
Small figurines would have occupied the niche. Worshippers offered food and objects as part of their daily ritual practice.
Nail holes above and beside the niche indicate garlands once hung there. A chipped edge marks the original placement of the altar slab, which excavators recovered. Conservators plan to reinstall it during restoration. Wall projections suggest the niche was once enclosed, and traces of paint remain visible.
Comparable household shrines are known from Roman cities, such as Pompeii, which were buried by the eruption of Mount Vesuvius. Researchers said this example is unique north of the Alps.
Cologne, known in Roman times as Colonia Claudia Ara Agrippinensium, was one of the empire’s key settlements along the Rhine frontier. The ongoing excavation continues to reveal how public authority, engineering skill, and private devotion once shaped life in the ancient city now hidden beneath modern streets.
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