Where’s the frontier? If you were Rome, it was where the barbarians lurked, those peoples who failed to see the benefits of living under Rome’s wise rule. If you were one of the Germanic tribes, it was the place you massed before attacking the Romans and reminding them who really owned the place. If you are a modern person, it is the area called the limes, the line of civilization and Roman ruins that demarcates civilized Europe from those people over there.
I’ve tramped the Limes from Castra Vetera to Augusta Vindelicorum east to Vindobona, Aquincum, and a few other places. “And I’ve tramped Britain and I’ve tramped Gaul/ and the Pontic shores where the snowflakes fall/ As white as the heart of Lalage, as cold as the heart of Lalage,” with apologies to Rudyard Kipling. I’ve not reached the Pontic shores yet, and I don’t foresee doing so in the near future. But I’m quite familiar with the Roman frontiers in Central Europe.
Cologne, Xanten, Trier, Mainz, just north of Frankfurt, down towards the Alps on the Rhine, along the Danube at Regensburg, under what’s now Vienna and Budapest… Dig a hole and you’ll find Rome. Until the 1800s it was even easier, especially in Hungary and parts east, because so many things remained above ground, lightly looted for stones but otherwise untouched. Then along came the modern tractor, and away went the ruins, because it’s easier to plow over than around and who needs those rock lumps when the collective farm demands more acreage, Comrade! And anyway, empires are bad. The future is what matters.
Rome wanted a secure border. The peoples moving out of Central Asia and northern Asia wanted space, and eventually trading goods. Rome sort of won a few rounds, but as we know, a lot of things combined so that in the end, numbers won out and the “barbarians” overran the western Roman Empire. People kept on living in the former Roman sites, with one notable exception. Xanten was abandoned and no one moved back in, preserving it in unusually “pristine” condition for archaeologists.
Otherwise the barbarians looked at what Rome had left and admired it. Some of them wanted to copy it. Happily, a relatively small group of people had actually preserved a lot of Roman ideas, instructions for building things and organizing people, and the Romans’ official language. Not the everyday koine Greek, but Latin. So the Christian Church began Romanizing the barbarians, or at least their leaders. In time, a leader of the Franks, Karl, or Charlemagne, would decide that he could recreate the Roman Empire but with the pope as the pontifex maximus.
Despite what a lot of educated people had assumed, between 476 and 800, the Roman Empire didn’t completely disappear. It faded into memories, and people used its remains for other things because the population crash in the 500s made life really, really hard. But Roman ideas and Roman technology remained around in small pockets and preserves, and people kept tinkering and discussing and improving until the Carolingian Renaissance and the High Middle Ages.
Most of what people recalled of Rome’s frontiers was on the Rhine. Why? Because of Julius Caesar’s little travelogue and political pamphlet. “Omnes Gallia in tres partes divisi est…” [waits for former Latin students to recover from memories] And the Rhine stayed a major trade route for such trade as there was. If you look at the maps, there are very few rivers that flow from the Alps to the north. The Rhine was where it was at. The Frankish kingdoms were on the Rhine, the Saxons and Bavarians inched Rhine-ward for a while, and civilization had bloomed on the Rhine. So did lots of little toll castles, and robber barons, but nothing’s perfect. Even Rome hadn’t kept everyone peaceful and honest.