2,000-Year-Old Roman Bridge Posts Reemerge from Riverbed

Archaeology Magazine ^ | September 19, 2025 | editors / unattributed

[SunkenCiv]

Swiss archaeologists gained new insight into Roman engineering and provincial infrastructure when the remains of a 2,000-year-old bridge reemerged from a former riverbed during modern construction near Aegerten in the Canton of Bern, The Miami Herald reports. Workers uncovered more than 300 oak posts belonging to a wooden structure that once spanned the Thielle River, an important waterway during the Roman era. Dendrochronological analysis indicated that the bridge was first constructed around 40 b.c., shortly after the Roman conquest of the local Celtic Helvetti tribe. It was intermittently repaired and strengthened over a period of 400 years. The bridge once stood outside the gates of the small Roman town of Petinesca, modern-day Studen, and formed a vital part of the Jura Transversal, a major Rome trade, communication, and transportation route that linked strategically important Roman military camps and settlements. Archaeologists also retrieved a number of objects that had accidentally fallen off the bridge into the river or had been intentionally tossed in. These included horseshoes, axes, coins, keys, a fishing trident, and a remarkably well-preserved carpenter’s plane made of wood and iron. To read about what scientists have learned from Swiss ice cores, go to "History in Ice."

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TOPICS: History; Science; Travel
KEYWORDS: carpentry; dendrochronology; godsgravesglyphs; juratransversal; romanempire; switzerland; thielleriver

[SunkenCiv]

Wooden plane with inset iron blade

Archaeological Service of the Canton of Bern, Daniel Marchand

[SunkenCiv]

Excavation of closely spaced oak posts from the bridge, Aegerten, Switzerland

Archaeological Service of the Canton of Bern, Joel Furrer

[SunkenCiv]

Preserved tips of oak posts, Aegerten, Switzerland

Archaeological Service of the Canton of Bern, Joel Furrer

[SunkenCiv]

[ProtectOurFreedom]

“300 oak posts”

aka, “pilings.”

How did they sink pilings in a river bed without a pile driver and a barge? Did they build diversion dams? Engineers want to know.

[jerod]

There’s a reason why Roman structures are still plentiful to this day... They knew how to build stuff. Most, if not all of todays structures will not be around 2,000+ years from now... Actually... Lot’s of them won’t be around in 100 years.

[Larry Lucido]

You got me curious too. I just cut and pasted your questions as a search term. Some interesting discussion here.

https://www.reddit.com/r/explainlikeimfive/comments/1252per/eli5_how_did_people_build_bridges_over_deep_andor/

[Paladin2]

How the Roman Army built Bridges and Forts

https://www.youtube.com/watch?v=7ynOEJVjxqI&t=203s

[ProtectOurFreedom]

Thanks. You learn something new every day! Yes, caissons, diversion dams, and pile drivers were indeed used. I asked Grok:

The Romans were skilled engineers who developed ingenious methods to drive piles into riverbeds for constructing bridges, docks, and other structures. They used a combination of manual labor, mechanical devices, and practical knowledge of materials and hydraulics. Here’s how they likely accomplished it:

1. Site Preparation and Dewatering:
   • Cofferdams: Romans often built temporary enclosures called cofferdams around the work area in the river. These were made by driving wooden piles in a circular or rectangular pattern and filling the gaps with clay, earth, or other materials to create a watertight barrier. The enclosed area was then pumped or bailed out to expose the riverbed, allowing workers to operate in a relatively dry environment.
   • Diversion Channels: In some cases, they diverted the river’s flow using channels or temporary dams to reduce water depth and flow at the construction site.
2. Pile Construction:
   • Materials: Piles were typically made of durable hardwoods like oak or alder, sometimes tipped with iron to aid penetration into the riverbed. The wood was often treated or selected for its resistance to waterlogged conditions.
   • Sharpening: The ends of the piles were sharpened to a point to ease penetration into the riverbed’s sediment or gravel.
3. Driving the Piles:
   • Manual Labor: Workers used heavy mallets or hammers to manually drive piles into the riverbed. This was labor-intensive and required teams of workers to strike the piles rhythmically.
   • Pile Drivers: The Romans are credited with early forms of pile-driving machines. These devices used a heavy weight (often a stone or metal block) raised by ropes and pulleys, then dropped onto the pile to drive it into the ground. The mechanism was operated by human or animal power, with a frame or tripod supporting the pulley system.
   • Counterweights and Levers: In some cases, they may have used counterweighted systems or levers to amplify the force applied to the pile, making the process more efficient.
4. Adapting to River Conditions:
   • Riverbed Assessment: Romans likely assessed the riverbed’s composition (e.g., sand, gravel, or clay) to determine the best pile length and driving method. Softer beds required longer piles to reach stable layers.
   • Anchoring: Piles were sometimes driven at angles to resist lateral forces from river currents, ensuring structural stability.
5. Examples and Evidence:
   • Trajan’s Bridge (101–106 CE): Built across the Danube River, this bridge used timber piles driven into the riverbed to support massive stone piers. The cofferdam technique was likely used to create dry working conditions.
   • Vitruvius’ Writings: The Roman architect Vitruvius described pile-driving techniques in his work De Architectura, mentioning the use of cofferdams and mechanical devices for foundation work in water.
   • Archaeological evidence, such as preserved wooden piles found in Roman bridges and wharves (e.g., in the Rhine River or London’s Thames), confirms their use of these methods.
6. Engineering Ingenuity:
   • The Romans’ understanding of hydraulics and material strength allowed them to adapt their techniques to challenging environments. Their ability to coordinate large workforces and use simple but effective tools was key to their success.

In summary, the Romans drove piles into riverbeds using cofferdams to manage water, manual labor and early pile-driving machines to insert wooden piles, and careful planning to ensure stability. Their engineering prowess, as seen in structures like Trajan’s Bridge, demonstrates their ability to overcome the challenges of working in river environments 2,000 years ago.

[SunkenCiv]

Thanks!

I think there’s a description of bridging the Rhine in Caesar’s Commentaries on the Gallic Wars. He built and dismantled two such Rhine bridges.

[rustling sound]

https://standardebooks.org/ebooks/julius-caesar/commentaries-on-the-gallic-war/w-a-mcdevitte_w-s-bohn/text/single-page

[snip]

Caesar, for those reasons which I have mentioned, had resolved to cross the Rhine; but to cross by ships he neither deemed to be sufficiently safe, nor considered consistent with his own dignity or that of the Roman people. Therefore, although the greatest difficulty in forming a bridge was presented to him, on account of the breadth, rapidity, and depth of the river, he nevertheless considered that it ought to be attempted by him, or that his army ought not otherwise to be led over. He devised this plan of a bridge. He joined together at the distance of two feet, two piles, each a foot and a half thick, sharpened a little at the lower end, and proportioned in length to the depth of the river. After he had, by means of engines, sunk these into the river, and fixed them at the bottom, and then driven them in with rammers, not quite perpendicularly, like a stake, but bending forward and sloping, so as to incline in the direction of the current of the river; he also placed two other piles opposite to these, at the distance of forty feet lower down, fastened together in the same manner, but directed against the force and current of the river. Both these, moreover, were kept firmly apart by beams two feet thick (the space which the binding of the piles occupied), laid in at their extremities between two braces on each side; and in consequence of these being in different directions and fastened on sides the one opposite to the other, so great was the strength of the work, and such the arrangement of the materials, that in proportion as the greater body of water dashed against the bridge, so much the closer were its parts held fastened together. These beams were bound together by timber laid over them in the direction of the length of the bridge, and were then covered over with laths and hurdles; and in addition to this, piles were driven into the water obliquely, at the lower side of the bridge, and these serving as buttresses, and being connected with every portion of the work, sustained the force of the stream: and there were others also above the bridge, at a moderate distance; that if trunks of trees or vessels were floated down the river by the barbarians for the purpose of destroying the work, the violence of such things might be diminished by these defences, and might not injure the bridge.

Within ten days after the timber began to be collected, the whole work was completed, and the whole army led over.

[/snip]

[SunkenCiv]

/bingo

[SunkenCiv]

Thanks!

[doorgunner69]

They don’t build them like they used to......

[SunkenCiv]

Oh, hey, great choice! There’s at least one of his (including on FR) about the later permanent bridge Trajan had built over the Danube. The last traces of that one got removed (explosives) during the 20th century to simplify modern ship traffic.

https://freerepublic.com/tag/garrettryan/index?tab=articles

[SunkenCiv]

https://freerepublic.com/focus/chat/4341715/posts?page=10#10

[SunkenCiv]

Modern bridges are unlikely to be around as long because they get torn out and replaced. There’s a place not all that far from here that, since I was a kid, has had three bridges one after the other, and I’ve driven on all of them at one time or another.

The first one I remember was probably the second or third one in that place, if not fourth or fifth. Early bridges were (like the first roads, rail ties, log cabins, houses, etc) built of ready-to-hand timber. The last of the old stand stuff was cut down not long before WWII.

Down by one of the big hotels in Grand Rapids there’s an historical marker about a massive logjam that happened in the 19th century, miles upriver. Grand Rapids sprang up in sort of hook in the Grand River. One of the old lumber barons heard the familiar sound of the logjam letting go and took his horsedrawn up and down with alacrity, shouting at everyone to get off the bridges (all of them were timber). The immense volume of still-tangled logs came through and took out all but one of them.

Seems like a great vignette for a period-piece movie. CGI. Logjam so high that the other bank and its structures can’t be seen...

[Larry Lucido]

"Caesar, for those reasons which I have mentioned, had resolved to cross the Rhine..."

[SunkenCiv]

https://getyarn.io/yarn-clip/3a57140b-5fcc-46d3-92ad-676d0b5d2175

[ridesthemiles]

LET’S SEE AI TAKE OVER THAT SKILL-————

[ProtectOurFreedom]

Thanks, SC! Great and very interesting excerpt.

Interesting bit --> "...there were others [piles] also above the bridge, at a moderate distance; that if trunks of trees or vessels were floated down the river by the barbarians for the purpose of destroying the work, the violence of such things might be diminished by these defences, and might not injure the bridge."

They should have had Caesar in charge of building the Francis Scott Key Bridge in Baltimore.

A friend is heavily involved in the replacement bridge and they are going to install much stronger defenses on both sides of the bridge to defend against "the violence of such things."