The Battle Against Rome: Rebellion of the Germanic Tribes CC

Teutonberg forest wasn't so much a battle as it was a running fight in terrain that the legions were completely unsuited to fighting in (dense forest with narrow game trails).

Going from memory here on out, so inaccuracy might be a small issue. But let's set the scene:

Three roman legions and a host of conscripts, volunteers, whores (laundresses, rather), and an experimental cavalry unit were crossing the river Rheine, which they'd lost to the Germanic tribes some time before. They were in "safe" territory and their legate, Gaius or Publius Varus (I don't rightly remember his first name), was well known as a slack hand at discipline, so he wasn't marching them in formation and the lines stretched for miles, without any separation between legions, recruits, or anything. The only unit that was maintaining cohesion and something approaching roman military discipline were the light cavalry who were completely out of their element.

As they continued marching on a dirt path through Teutonberg forest toward the river Rheine, they churned the road into deep sucking mud as the weather turned on them. The recruits began abandoning their equipment, as a legionary shield was heavy to begin with (being made of bronze or iron rimmed hardwood) even before it got waterlogged. Their bowstrings wet, the archers packed away their bowstaves and never drew a shield or gladius, instead believing themselves safe and close to camp for the night they were only armed with their eating knives and whatever trophies they'd collected individually.

The weather continued to worsen as they marched, stringing their lines out even further - and in the days before radio and cellphones, this proved deadly when a host of screaming Germanic tribesmen came howling out of the forest and started rolling them up along the entire 10+ mile long line of roman legionaries. They were smart about it too, and their first targets were the supply wagons at the rear of the roman train.

Varus managed to regroup after the Germans withdrew and he directed the survivors to build a fortified camp for the night. This too was deadly for the romans as the Germans used their own captured javelins to rain hell down on the camp from nearby bluffs - Varus chose his position poorly, in a valley between a rise of hills on one side and bluffs on the other. The rain of javelins, rocks, and even legionary gladiuses continued through the night, inflicting light casualties but further tiring and demoralizing the roman force.

Now, one thing to remember here is, this was far from the glory days of Rome. Those days were in the future yet; Rome had only been an empire for about 30ish years at this point.

Anyway, the day after the all night bombardment of the Roman camp, the weather continued to deteriorate, prompting the Germans to withdraw, leaving some scouts and pickets to watch the romans. This allowed Varus to escape to the plains, but not before the Germans started harassing him with hit and run attacks again. So instead of staying on the plains, Varus made the colossally stupid decision of marching through yet another heavily wooded area. In the middle of a storm. He ended up going for a narrow track between the forest and a marsh, that culminated on top of a hill that he wanted to set up camp atop. Unfortunately for him, he never made it. He was ambushed at the foot of the hill after arriving to find that the Germans were already on top of it.

It was during this death match that they suffered the final betrayal, as all of their cavalry up and rode away. They didn't make it far though, and we're cut down by German cavalry elements a couple of miles away from the main body of the legions.

Varus and three roman legions tried like hell to take that hill, but they failed and were slaughtered or enslaved there to the last man.

I wouldn't personally call this the absolute worst defeat of the Roman Empire, but it's close. Six or seven entire tribes of Germans taking on three legions and assorted others kept the numbers reasonably even. For the worst defeat, I'd have to say Phillip of Macedon taking out an entire roman legion with about two battalions of cavalry long before Teutonberg forest was a thing.

That defeat managed to happen where Rome should have held every advantage, from the terrain to the freshness of the troops and the cooperative weather, not to mention the steep, STREP numerical superiority.

That, to me, is a worse defeat than the longest unlucky string in the history of Rome.

Edit to fix: it was Phillip of Macedon, not Alexander. I can't brain today, I has the dumb.