To the Limes belonged a Palisadenzaum, behind it were watchtowers. The towers were just so far apart that they were in sight. So the soldiers could, in case of danger, quickly pass the alarm. They did this with trumpets, mirrors, smoke or flares with torches. The alarm went not only to the neighboring towers, but also to the camps with the soldiers in the castles. To ward off an attack, soldiers from the fort had to come to the rescue.