It was the year 9 AD. when the governor of Germania Publius Quinctilio Varus decided to enter Germania, crossing the Rhine to carry out administrative tasks, collecting taxes from the different Germanic tribes, thus reaffirming the influence of Rome in the westernmost part of Germania.
With little strategic knowledge and no combat experience, Varus saw fit to take with him three of the best legions in Rome at that time - the XVII Novaesium, the XVIII Castra Vetera and the XIX Oppidium Ubioum.
By carrying the bulk of these three legions, the march would slow down too much as it crossed the Germanic forests, causing delays in the Roman column and leaving the bulk of the army exposed. As if the errors of the incompetent Varus were not few, the Cheruscan Arminius, who commanded a detachment of Roman auxiliary cavalry made up of Cheruscans, took advantage of the situation to betray Varus, inform the Germans of the situation and attack the Romans in the Teutoburg Forest.
The battle lasted four days and the three legions along with other auxiliary detachments were annihilated by the German forces. Varo himself took his own life in the face of such a disaster.
The legions lost in Teutoburg were never rebuilt and, due to the betrayal of Arminius, the auxiliary units stationed in the provinces, formed up to this point by natives of the province in question, were sent to other places that there was no patriotic feeling of uprising against Rome, thus avoiding future betrayals.