Top of the Line Roman Legion - how late in history before they would be beatable?

The Roman military machine ruled the Western World for a long, long time, as we know, but eventually the Empire fell. Europe spent a few centuries sorting itself out, then got on about the serious business of warfare.

So, my question - at what point in history (in Europe, specifically, we’ll leave China and Japan aside for now) would a top-tier Legion face stiff opposition if they were transported forward in time? Was there any military force prior to gunpowder (or even into the early years of gunpowder armies) where a Legion would face a probable defeat? What would be the defining factor in that defeat - equipment? Strategy? Massive outnumbering?

It seems to me that until the time of gunpowder, the Romans wouldn’t really be facing anything they were unfamiliar with (even crossbows are just small “seige engines”), and their training and organization might give them the same kind of edge it did throughout their history against the greatest armies in history.

I guess a less-awkward way of putting it would be - how far along in history would they be effective?

RelatedSDMB discussion here re legion capabilities.

Re your OP qualification about gunpowder use being the demarcation end point it’s use came much earlier than you might imagine in warfare starting in about the 11th century. If the Legions lasted to approx AD 470 that’s only about a 600 year window that you can look for competitive non-gunpowder armies.

Legions were beatable, and quite often beaten, even back in Rome’s heyday, sometimes by well led forces of inferior numbers. Ever hear of Hanibal, or Vercingetorix? They may not have won their wars, but they won battles alright.

Roman legions got defeated all the time in the ancient world. The Gauls defeated legions. The Samnites defeated legions. The Carthaginians defeated legions. At various points, even escaped slaves defeated legions. The legions were good, but they were certainly beatable.

The decendents of the legions the tagma were able to defeat pretty much all of their opponents and and the Empire lasted into the gunpowder age. Indeed it was gunpowder weapons which ended the Empire in 1453. Till the late middle ages, no European military was able to consistently best the Romans.

As it is we have an answer to the OP, the legions were able to (barely) hold off the Persians and the Bulgars and Avars, but could not withstand the Arabs. The legions were abolished around that time.
I do think your restrictions to Europe is myopic, the greatest challenge the late Empire faced was from the East.

Well, here is an example of them being beaten in 9 CE. Here is one from 53 BCE as well. As other have mentioned, the Roman legions were beaten quite often throughout history. They certainly were never unbeatable. I can think of at least a dozen times off the top of my head where legions were beaten in their hay day, and I’m not historian. The Romans won more than they lost, and certainly Romes war machine was top notch…plus they were pretty tenacious when there was a large prize at stake, and often wouldn’t take a single defeat or even a series of defeats as the end of the story.

Well, yes, they were sometimes beaten, but the Roman military was never beaten until the legions turned to foreign mercs.

Gunpowder was for show and sieges until the late 16th century. But yes, effective cannons and massed musketry is pretty deadly.

The English/Welsh Longbowman might have been able to do it.

Well, the late Byzantines, altho certainly a successor state to Rome, certainly didn’t have much in the way of citizen soldier legionnaires.

Not Western, but I think the Mongols would have beaten them through tactics, strategy, firepower.

The Goths absolutely beat the stuffing out of several legions in 378; the slain outnumbered the survivors.

I think that a more interesting question would be: “at what point did the Roman Empire cease to have an economic system that could fund a large standing army”. The legions were a product of an economy that could fund a lot of standardized weaponry (swords, armor, hobnailed sandals), and recruit career soldiers. These units fought well (usually) because they were commanded by well trained officers. The whole Roman military system went into decline when native-born Romans ceased joining the legions, and economic difficulties made paying the soldiers difficult. Its hard to maintain an army if the soldiers are pillaging the country-because they haven’t been paid. The end finally came when most of the soldiers were barbarians, and started attacking Rome itself.

I can’t recall the guys name. But there was a Barbarian mercenary that became a high ranking officer in the Roman Legions. After a few years he turned on Rome and lead a Barbarian army against them. He knew all the Roman legion tactics and really kicked their asses.

The History channel had a special on this guy. He ambushed the Roman Legion in a German forest. Killed them and nailed their bodies up in trees as a terror tactic and warning to other Roman soldiers.

That last point is worth emphasizing. Hannibal beat the legions of the Roman Republic over and over and over again–crushing victories, against superior numbers of Romans. But the Romans were an extraordinarily bloody-minded bunch and simply refused to let having a few armies slaughtered here and there stop them. The Romans eventually won the war, and later went on to stomp Carthage into the ground. This “losing the battle doesn’t mean we’ve lost the war” attitude was something the Romans were famous for.

The Byzantines were not a successor state to the Romans, they were the Romans.

The theme system was certainly more akin to the pre Marian Roman army, but they did have a large professional contingent.

That sounds like Arminius, who led the Germanic tribes to an overwhelming victory over the Roman legions under the command of Varus in the Battle of the Teutoburg Forest (also linked by XT above). I don’t know about nailing bodies on trees, but the battle did give rise to the famous quote from Augustus: “Varus, give me back my legions!”

I’d guess that the legions might still be effective up until the advent of heavy cavalry sometime in the early middle ages. Heavy cavalry would have pretty much crushed legions.

I suspect that a well disciplined legion would give a pretty good account of itself if faced with a Saxon/Viking shield-wall. After all, in one fashion or another, warfare had been some variant of it from at least Greek days.

Two significant changes to infantry weapons were the introduction of steel and the introduction of firearms. Romans already had steel. So given their excellent training and leadership, a good Roman legion could take on any infantry army up to late 16th century or so.

Cavalry is a bit more difficult. AFAIK, Roman legions never faced an enemy who used stirrups. On the other hand, late-medieval / early-renaissance mercenary companies armed with pikes handled cavalry charges just fine. While Roman javelins would have been a little short for the job, I am sure that they would have improvised.

Unlike others, I don’t think that the longbow would have been an issue either. It was mostly effective against heavy cavalry and light infantry. Legionnaire’s shield could have stopped an arrow at all but very short range, and he would have known how to use it properly.

A scutum? Made of wood, canvas, and leather?

They faced heavy cavalry a number of times and eventually added their own version. Though they took their share of defeats facing them, they adapted reasonably well - even heavy cavalry is not going to invariably smash solid, prepared ranks of infantry.

What they did not face, as noted above, was cavalry with full stirrups. But the impact of the stirrup seems to have been a bit over-hyped by earlier academics ( and has since been challenged ). Though undoubtedly superior technology, the lack of them in no way prevented the use of shock cavalry. They simply used other methods to ground lances ( like saddle loops ) and maintain stability ( like high cantles on saddles and leg straps ). More cumbersome than stirrups to be sure, but reasonably effective.