Construction of a new boathouse on the Rhine in Kaiseraugst, outside Basel, Switzerland, has revealed the remains of a previously unknown Roman amphitheater that is the youngest that has ever been found in the Empire. Aaargau Canton archaeologists started excavating the site last month expecting to encounter material remains from a quarry that was abandoned in Roman times. They were surprised to find an oval ring of walls instead.

The walls encircle a hollow of the abandoned quarry and are about 165 feet long and 130 feet wide. A large entrance gate flanked on each side by smaller entrances was unearthed on the south side. A sandstone block from the threshold of another gate was found on the west side. Some of the walls have surviving plaster on the interior. Of the wooden bleachers only the impression of wooden posts they were built on remain.

The structure was adjacent to the Castrum Rauracense, the military fort built near the city of Augusta Raurica in around 300 A.D. when the Roman army had to redraw its defensive lines after the loss of Upper Raetian Limes in the Germanic invasions at the end of the 3rd century. The location next to the fort, the use of the abandoned quarry and the building materials use all point to the amphitheater having been constructed in the 4th century, which makes it the youngest known.

The good folks of the Basel Rowing Club will benefit greatly from this find. The plans for the boathouse have been redesigned to include the amphitheater’s remains. They will be left in situ, protected by a barriers while the new building is erected above them creating the coolest boathouse of all time.