Großkrotzenburg was the site of a Roman fort, built around 140 AD. A few years earlier, the Romans had completed the Odenwald Limes and also built a fort in Obernburg am Main. Between Obernburg and Großkrotzenburg, the Main marked the border to free Germania. There were no stockades; Left Main forts near Niedernberg and Stockstadt were sufficient for security.
The interesting question is why the Romans used the Main as a border for 40 km from Obernburg and then, of all places, built a bridge near Großkrotzenburg and then a fort on the right side of the Main, from which the Limes continued.
The Romans wanted to avoid the dense and inaccessible Spessart when building the Limes. The Roman legions could not develop their fighting strength in Germanic forests. In 9 AD the Germans inflicted a devastating defeat on the legions of the consul Varus in the Teutoburg Forest.
The Romans built their Limes lines as straight as possible so that there was visual contact from the watchtowers and the Limes could be defended more easily. Around the year 140 AD. a simple fort already existed in Altenstadt (Hesse). Großkrotzenburg is almost due south of Altenstadt. The Limes line between Großkrotzenburg and Altenstadt could therefore largely be built in a straight north-south line.
The Romans wanted swamps, moors and damp alluvial forests to stretch in front of the Limes, because no attacks are possible in the deep soil. From Großkrotzenburg, the Limes leads dead straight through the “Schilfläche von Großauheim” over to the formerly swampy “Wolfganger Lache”. Then the Kinzigaue with the permanently wet alluvial forests is crossed until the Roman fort in Erlensee is finally reached on dry feet.