The origins of the ancient site of Vindonissa date back to a Celtic settlement controlling the strategically important position at the confluence of the Aare, Reuss and Limmat rivers. During the Alpine campaign of Emperor Augustus in 15 BC, Roman soldiers established a military post here which was later developed into a legionary camp under Emperor Tiberius (14–37 AD).
The camp was some 20 hectares in size and was initially constructed by the 13th Legion out of wood and clay. The 21st Legion then gradually replaced and extended the existing buildings with stone structures. The last unit to occupy the site was the 11th Legion, which was withdrawn by Emperor Trajan into the Danube region in 101 AD. As time went on, a civil settlement became established outside the legionary camp and this continued to exist after the troops were withdrawn.
The legionaries of Vindonissa had a key role to play not only in the Roman conquest of the region on the right bank of the Rhine but also in establishing provincial structures in the southern Germania Superior. There was no place between the Alps and the Rhine where Rome's presence was more powerful. As many as 6,000 legionaries and officers also brought their Mediterranean lifestyle and civilisatory achievements with them, acting as a kind of "motor of Romanization".