Most likely Roman emperor Claudius transferred the legion to Mainz in Germania Superior.It is unknown when this happened although it was probably in 41 AD.It replaced XIV Gemina, which was now fighting in Britain. However. Some people think that the legion was transferred in 39 AD, when emperor Caligula waged war against the Germanic Chatti. While stationed in Germania the Fourth shared the fortress with the recently founded XXII Primigenia. The younger unit occupied the less honorable left-hand side, whereas IV Macedonica was living in the right-hand side. After the Battle of Teutoberg Forest the Legio IV Macedonica