The Pannonian Limes is a part that is mostly found in Hungary from the Roman front line known as the Danubian Limes, a line of castles and fortifications along the Danube River. The fortification line included guard towers, legionnaires camps (castra) and forts (castella).
The plaques are located in the March 15 square in Budapest where one of the camps stood, describing the relative location of the camps along the Danube which is also drawn on the sidewalk.
The current plaque shows Aquincum, the Roman name of the city that is where Budapest city is today. The military camp in Aquincum was established in AD 40
In the next photo taken on the same day, part of the line of fortresses was seen, with the route of the Danube River between the various plates Click for a larger image