For those reasons, Drusus was sent to Illyricum with proconsular "imperium maius", and would be governor there from AD 17 to 20. Since Germanicus had left the Rhine in AD 16, the German tribes that formerly fought alongside each other against the Romans had turned on each other. The two major forces in the region, the Marcomanni under king Maroboduus and the Cherusci under Arminius clashed and, after an indecisive battle, Maroboduus withdrew to the heart of his kingdom in the forests of Bohemia. Before that, two tribes (the Semnones and Langobardi) had defected to Arminius.