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 Alta Ripa, the Roman name of the fort in Tolna, Hungary. The fortress was probably built in the first century AD and existed until the end of the fourth / beginning of the fifth century AD.
Notice the two lines representing the Danube River on the right side of the plaque.
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