The Bora: The Wind That Decided a Roman Battle
- Adam Lofthouse
- Jul 6
- 4 min read
In my last post I wrote about the Battle of the Frigidus, and I promised to come back to one detail that has stuck with me ever since I first read about it — the wind. Because the more you look at the Frigidus, the more you realise that the deciding factor on the second day of battle wasn't a general or a legion or a clever bit of tactics. It was the weather. A wind so violent that men on both sides believed a god had sent it. That wind still blows today, and it has a name: the bora.
What is the bora?
The bora is a cold, dry wind that comes roaring down from the northeast, off the high limestone plateau of the Karst and down towards the Adriatic. It's what's known as a katabatic wind — cold, dense air that builds up over the mountains and then pours downhill under its own weight, gathering speed as it falls. By the time it reaches the lowlands it can be moving at genuinely terrifying speeds. Gusts of over 150 kilometres an hour are common. In the worst of it, in places, the wind has been clocked above 200.
If you've never stood in a wind like that (like me), it's hard to picture. This isn't a stiff breeze that makes you turn your collar up. This is a wind that knocks grown adults off their feet, that can flip a car, that howls for days without pause.
A wind that shapes a whole region
What I loved about researching the bora — as a writer who spends his days trying to make the ancient world feel real — is that it isn't some freak event dredged up from a single battle. It is woven into the daily life of that whole corner of the world, and always has been.
In Trieste, gusts routinely top 120 kilometres an hour. When the bora is really blowing, the city stretches chains and ropes along the pavements so that people have something to cling to as they walk. Along the coast, the old towns were built deliberately dense, their streets narrow and twisting, to break the wind's force. Climb up into the villages of the Karst and the Vipava valley and you'll see houses with heavy stones laid across the roof tiles — because otherwise the bora simply peels the roofs away.
This is a landscape that has organised itself around a wind. That tells you everything about the kind of force we're talking about.
The bora goes to war
Now put an army in that valley.
In September AD 394, the Vipava valley — the Frigidus to the Romans — was the setting for the civil war that would decide the fate of the empire. On the first day, Theodosius's eastern army bled itself white against the Western line and very nearly lost. On the second day, the bora came.
It screamed down the valley from the east, straight into the faces of Eugenius and Arbogastes's men. It filled their eyes with dust and grit. And according to the legend that grew up afterwards, it did something stranger still — it caught the Western soldiers' own arrows and javelins in the air and flung them back at the men who had thrown them. Their line buckled, then broke. By the end of the day the usurper was dead and Theodosius was master of the Roman world.
To the Christian writers who told the tale, this was no accident of geography. Theodosius, they said, had spent the night in prayer, and God had answered him with the wind. The bora became proof of divine favour — the breath of the Christian God scattering the armies of the old gods. (I'm not a man for religion, and I certainly wouldn't credit a natural weather phenomenon to any God, but the Romans were very different people to me!)
History or legend?
Here's the part I find most interesting.
The earliest Christian source to mention the wind, Bishop Ambrose of Milan, actually said it blew before the fighting, demoralising Theodosius's enemies rather than winning the battle outright. It was the poet Claudian who moved the wind to the dramatic climax, and he seems to have borrowed the image of arrows flung back on their owners from an old account of the Battle of Cannae. So the version we all know and love, the wind striking at the perfect decisive moment, may owe as much to poetry as to fact.
But the bora is real. Historians can argue about whether it fell at the start of the battle or the end, whether it decided the day or merely helped. What nobody disputes is that on that ground, in that season, a wind fierce enough to change a battle is entirely believable.
And that's why it makes such wonderful material for a novelist. The bora sits right on the line between the natural and the miraculous — a wind that men could feel on their skin and yet also believe was the hand of heaven. When you're writing a world where people genuinely thought the gods walked among them, that's gold.
I wrote the Frigidus, wind and all, into Barbarian and the Throne, book four of the Shadow of Rome series, out on 24 August. If you enjoy Roman historical fiction in the vein of Simon Scarrow, Ben Kane, Conn Iggulden or Harry Sidebottom, you can pre-order it now.
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