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 Carnuntum, the Roman name of the multi-period legion camp in Bad Deutsch-Altenburg, Austria. The camp was established around 70 AD, and existed until the end of the fourth century AD. Beginning in the second century AD, the camp also served as the administrative center of the Pannonia region.
Notice the two lines representing the Danube River in the top-left corner of the plate.
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