Vindonissa

The only Roman legionary fortress of the 1st century AD in Switzerland, located at modern Windisch at the confluence of the Aare and Reuss rivers. Established as a military post around 15 BC during Augustus's Alpine campaign, it grew into a full legionary camp by 15 AD, covering 20 hectares with a 1.8-km encircling wall. The site hosted Switzerland's largest Roman amphitheatre, seating 10,000 spectators. A 1.2-mile Roman underground water canal still functions today, supplying the later Konigsfelden Monastery. The last garrison, Legio XI Claudia, departed in 101 AD when Trajan redeployed it to the Danube region. Listed as a Swiss heritage site of national significance.