Saalburg

This is the entrance of the Saalburg next to Bad Homburg (Germany). 
It was a roman fort where on the best days in the mid-2nd century around 2000 soldiers were living. 
Its placed on the Limes, a germanic border defence, where the roman empire was batteling the germanic tribals.
Around AD 135 the Second Raetian Cohort was stationed at the Saalburg and converted the old timber fort into a larger cohort fort.