The Roman Bridge in Augusta Treverorum (Trier)
I asked Aelius Rufus to give us a tour of the Roman Bridge in Trier. Hallo Aelius.
Salvete, Gabriele and dear readers. You're some friend, making me dig out those dusty old history books so I can fill your readers in on the two bridges that were there before the one they built in my time.
Well, let's get started. Augusta Treverorum, what is now called Trier, is situated on the right side of the Moselle though today its spreads to the other shore as well, Gabriele tells me. The river widens into a valley here, framed by hills which are mostly wood covered, sprinkled with the occasional vineyeard - not enough of them for my taste - or grazing ground. But already the Roman town encroached up the hills looming behind it; the arena is situated on one of them, for example.

The Roman bridge seen from the direction of Koblenz upriver
(The photos were taken during a Moselle river cruise.)
Trier was founded in 17 BC, and the first bridge spanning the Moselle dates to that time. The deified Augustus had just made the last of his enemies fall upon their swords or snakes and won the civil war. He now could concentrate on the neglected provinces. He sent his friend Marcus Vipsanius Agrippa to kick some German marauders out of Gaul (what is the matter with those ancestors of yours?) and bring the infrastructure up to Roman standards. You know, us soldiers want nice roads to march on, not tree roots, swamps and undergrowth.
We also don't mind bridges instead of splashing through fords, but I suspect the merchants were the main reason to set up a dry crossing of the Moselle. The old ford was on the interstate from Marseille to Mainz, a very important road, and already guarded by some soldiers stationed in a fort on the Petersberg hill on the east side of the river. Now Agrippa not only ordered a bridge to be built but also founded the a new town in the name of Augustus - Augusta Treverorum (after the tribe of the Treveri living in the area) - on the right shore where the valley widens.
Getting closer to the bridge
The town was planned on the drawing board and has a very regular street pattern, not very different from our forts. Same everywhere in the Empire, but the good thing is you can't get lost in an unknow town or castellum once you've memorised the standard Roman street map. Augustus had guessed right; the town lies in an excellent spot where a major road and a river cross, and prospered.
That first bridge was a wooden pile bridge. The Romans still make those sometimes so I know how it's done. Long, massive poles, usually of oak, were rammed deeply into the soil beneath the bridge until the grip of the soil around the piles would support the load of the superstructure; that is, the supporting beams and the deck. Gabriele tells me that remains of those poles have been found in the riverbed in AD 1963, and were dendrochronologically dated to 17 BC (and you tell me Latin is complicated; that word is worse than those languages they speak around Caerleon up in Britain). But it's fascinating that you can tell such things from an old, wet oak bole.
Closeup of one of the Roman pylons, seen from downstream.
Notice the sharp wedge that was intended to break ice shoals in spring, and prevent flotsam
like broken trees from cluttering up and damaging the bridge.
In the long run, wooden bridges aren't good enough for real Romans, though. The first stone bridge, about 8 metres downriver from the present one, dates to AD 71. There is an earlier date (AD 45) floating around on that place called internet, but that looks like the result of several website scribes copying an outdated manuscript. The date of AD 71 is dendrochronologically confirmed now.
That puts the construction of the stone bridge to the time of the Emperor Vespasian, shortly after the Batavian rebellion, the big mess along the lower Rhine that eventually spread to parts of Gaul. You may remember that one of the battles of that uprising - after the Treveri joined the fun - took place around and on the bridge of Trier. Took the Romans their sweet time to defeat the rebels, too, but they managed in the end, thanks to Cerialis. I admit I had to read Tacitus' account twice to make sense what legion was where and who was fighting whom. That guy never heard about 'linear writing', I suspect. Or maybe the Romans indeed didn't know where their legions were and whom they supported. But that's something us auxiliaries only talk about when no Roman centurion is around. So don't tell the wrong people I said that.
The wooden bridge survived, but it fit well with Vespasian's rebuilding program (remember the Isis temple in Moguntiacum), to sponsor a new and better bridge to show the inhabitants of Augusta Treverorum that being part of the Roman Empire had its advantages. The town got a pretty new forum with a stone basilica as well and some new insulae with water flushing, so everyone said they were very sorry about the mess and would not revolt again.
The bridge seen from the direction of Luxembourg downriver
If you wonder how a stone bridge can be dated with a method in need for timber, there's an explanation: timber was used during the construction process of the pylons. The same method would be used for the second stone bridge which I helped building - as far as the Romans trust us auxiliaries with the job; it was mostly shoveling mud and carrying stones. So I know how it's done.
The Romans first erected a casing of double cantilevered retaining walls filled with clay, then pumped the water out of the encased area, dug out enough soil to reach the rock beneath and set up a solid stone foundation on which the pylons rested. The whole was fixed with opus cementitium. The bridge had 13 stone pylons with a timber superstructure. Remains of those wooden retaining walls, together with the stone foundations, have been found in the Moselle riverbed where they can still be seen at low water.
The third bridge, constructed in the same technique, can be dated to AD 144-157. The town had expanded considerably to about 5000 inhabitants and the old stone bridge was too small to deal with the increasing traffic (that's a very modern problem, Gabriele says). So our venerated Emperor Antoninus Pius decided to have an even larger bridge built. It was ten metres wide (the old one 'only' 6.5 metres).
Another photo of the bridge in the evening twilight
Those photos Gabriele took look a bit different from the bridge I know. Not the entire bridge spanning the Moselle is Roman, ony the pylons - the pillars made of the grey stone supporting the reddish brick archs - are still Roman and almost 1850 years old. Originally there had been nine pylons but only five remain; the others fell victim to the training of the Moselle after the Second Great War (what they call WW2). The Porta Inclyta, the bridge gate, had already been dismantled in the 19th century. Stupid people from the Future.
The pylons have a kernel of a mix of quarry stones and opus cementitum (a typical Roman technique) that is faced with large lava basalt cuboids we got from a nearby inactive volcano. They are connected by iron clamps; the whole thing, foundations and pylons, is 14 metres high and carries a wooden superstructure. That makes the bridge high enough so that the ships don't have to take down their mast when the water level is normal. The ships use sails for the voyage downriver; upriver they need to be hauled because of the strong current.
Closeup of a pylon; backside
I've been told that the wooden superstructure was replaced by brick archs in the 14th century, and later some Gauls tried to blow up the bridge with some odd black powder, but they only got the brick stuff down, not the part we built, neiner, neiner. Our pylons were still good to support another set of brick archs, and the bridge is still in use today.
The Roman Bridge in Trier is today part of the Unesco World Heritage, a list of famous historical buildings. Obviously being on that list involves getting a bit money, too, and with no emperors around to fund repairs that might be a nice thing.
Well, my friends, I've told you everything I know about the Roman Bridge in Augusta Treverorum, and I'll now cross that bridge into town and visit the baths. Tony .... oops, the venerated Antoninus Pius has sponsored a new and large bath, and you know how much I like those.
Oh yes, dear Aelius, I do know. At least I'll also know where to find you next time.