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 palisades; Left Main forts on the one 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 first built a bridge near Großkrotzenburg and then a fort on the right side of the Main from which the Limes continued.
When building the Limes, the Romans wanted to avoid the dense and inaccessible Spessart. The Roman legions were unable to develop their fighting strength in Germanic forests. In 9 AD the Germanic tribes 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. There was already a simple fort in Altenstadt (Hesse). Großkrotzenburg is located 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 moist floodplain forests to extend in front of the Limes, if possible, because attacks are not possible in the deep ground. From Großkrotzenburg the Limes leads straight through the “Schilflache von Großauheim” over to the formerly boggy “Wolfganger Lache”. Then the Kinzigaue with its permanently moist floodplain forests is crossed until the Roman fort in Erlensee is finally reached with dry feet.