8. The Battle Of Teutoburg Forest (9AD)
As the Roman Empire grew, it became over-reliant on 'barbarian' troops. As the Romans expanded east of the Rhine, Arminius, chief of the Cherusci tribe, who had been granted Roman citizenship, warned Varus, the Roman commander, of a minor uprising. Varus gathered his forces and began marching. Arminius had, in fact, formed an alliance with the major Germanic tribes and was leading Varus into an ambush. As the force entered Teotoburg Forest, Arminius slipped away and joined the tribal force. The 36,000 strong army was ambushed, and, because they weren't in battle formation, half of them were slaughtered. The remaining force continued but, after finding their route blocked, the slaughtering continued. 35,000 were killed. The Germanic tribes proved to be the undoing of Rome. While the area offered little in terms of economic prizes, it would have provided some stability on the northern front. A victory, as unachievable as it sounds, would have completed the incorporation of the lands east of the Rhine into the Roman Empire. Considering that's where some of the Germanic tribes, who damaged the Empire in later centuries, emerged, the Romans would have been in a much better position to quash these forces and provide more protection to Rome.