A Roman lararium (a private altar dedicated to the households guardian gods, the Lares) from the 2nd century A.D. has been discovered in Cologne. It is the first lararium found north of the Alps.Originally settled by the Germanic Ubii tribe, the Roman city was founded as Colonia Claudia Ara Agrippinensium in around 50 A.D. by the Emperor Claudius. He granted it full city rights, privileging it because his wife, Agrippina the Younger, was born there. It became the capital of Germania Inferior and was one of the most important cities of the empire north of the Alps.The house altar was discovered during an excavation in preparation for the new underground visitor space of the LVR Jewish Museum in the Archaeological Quarter of Cologne. Because the new underground tour goes deeper than is typical in downtown archaeology, the excavation has encountered the remains of early Roman buildings, including a monumental apse (the semicircular end of a building) of a multi-aisled building from the 4th century and the 2nd century Praetorium, the villa of the Roman governor.The remains survived due to a fluke of location. They were built on the slopes of the Rhine, and even in Roman times parts of the buildings were covered up by earth embankments to protect from flooding. Because of the soil backfilling, later construction went up above the structures instead of razing them first. Normally only the foundations of ancient buildings are found, but at this depth in this place, whole building structures were discovered.The lararium was in the Praetorium. It is a deep arched niche on which figurines of the Lares stood. Families left offerings of food, flowers and other assorted objects to the deities on the altar. Remains of walls projecting from the sides indicate the niche was originally enclosed. There are also traces of paint stars are visible inside the niche. Nail holes were found above the arch and on the side of the niche where garlands were hung. Below the niche is a rectangular cutout line that marks where the altar slab was mounted. The slab itself was found in the excavation, broken off and displaced but still present.While household altars were common in Roman homes all over the Empire, their remains do not typically survive north of the Alps because masonry preservation especially of private dwellings is so rare. To have found not just a lararium in Cologne but one in such good condition is of great archaeological importance.The same excavation unearthed a staircase from the 1st century that connected a location near the Rhine shores with a higher level of the Praetorium. Only a section of the stairs remain, so its not clear where they ended or what they led to. These too are rare survivors and the stones from staircases like these were usually recycled in later construction.The city plans to restore the lararium, remounting the altar slab, and will make it, the staircase and the apse part of the underground route of the new museum. The route also includes a medieval goldsmiths workshop and remains of the citys Jewish quarter.