1,700-Year-Old Roman Bridge Discovered Beneath the Aare River in Solothurn, Switzerland

A Roman bridge in Solothurn, Switzerland, long suspected by archaeologists but never proven through physical remains, has finally been confirmed beneath the waters of the Aare River.

During an underwater archaeological survey ahead of the renewal of the SBB railway bridge, divers working for the Cantonal Archaeology Office of Solothurn identified wooden piles embedded in the riverbed near the Wengi Bridge. Samples from the timbers have now been dated to the fourth century AD, placing them in the late Roman period, when ancient Solothurn, known as Salodurum, was being reshaped into a fortified settlement.

The find gives archaeologists the first material proof of a Roman-era river crossing at a location that had long seemed almost inevitable. For years, scholars suspected that a bridge must have stood here. Now, after roughly 1,700 years underwater, part of its structure has been found.

Wooden piles reveal a lost Roman crossing

The remains lie a few meters upstream from the modern Wengi Bridge, around ten meters from the southern bank of the Aare. Divers documented a short line of piles, nearly two meters long, running in the direction of the current. The timbers probably belonged to a bridge pier, or pile bent, which once supported the upper structure and roadway.

The surviving posts are modest in size today, but their significance is far larger than their appearance suggests. Some are preserved to a height of about one meter and have a diameter of roughly 20 centimeters. Their dating confirms that they were part of a late Roman construction phase, not a later crossing.

Older reports had mentioned piles in this part of the river, but the current investigation allowed archaeologists to examine them closely and obtain datable wood samples.

Salodurum stood at a strategic bend in the Aare

The bridge makes sense within the geography of Roman Solothurn. The Aare winds strongly upstream of the city, but at Solothurn it narrows into a more constrained channel. For Roman engineers, soldiers, traders, and travelers, this was a practical place to cross.

That topography is reflected in the ancient name Salodurum, usually understood as the Latinized form of a Celtic place-name referring to a river narrows or “water gate.” The Romans founded the settlement around the early first century AD, probably around AD 20, as part of a transport system linking important centers of Roman Switzerland.

The newly confirmed bridge belonged to a long-distance Roman road that ran from Italy over the Great St Bernard Pass, crossed the western Swiss Plateau, and continued through the Jura toward the Rhine. Remains of this road had already been identified near Solothurn.

A bridge from the age of the late Roman castrum

The fourth-century date is important because it places the bridge in the same period when Salodurum was transformed from an earlier Roman settlement into a fortified castrum. Across parts of Roman Switzerland, the later empire responded to military pressure and political instability by reducing and fortifying urban sites.

A castrum was not simply a town wall. It was a defensive system. At Solothurn, the fortification protected a key crossing point on the Aare and helped secure movement through a region connected to wider imperial routes. The newly dated bridge piles do more than confirm an old hypothesis. They help explain why late Roman authorities strengthened Salodurum.

Beneath Solothurn’s later urban layers lies a Roman settlement whose position was chosen for movement, control, and access to the river.

Preserved by water, spared by chance

The survival of the wooden piles is a fortunate accident. During the Jura water correction works in 1969, the riverbed near Solothurn was dredged extensively. Many ancient remains could have disappeared. The late Roman piles survived because they stood in the protected area near the Wengi Bridge.

They will remain where they are. For ancient waterlogged wood, the riverbed can be the safest place, because constant moisture slows decay. Since the new railway bridge works do not threaten the timbers, archaeologists have no reason to recover them.

Further dives are planned. The known piles may represent only a small part of the original bridge structure. If additional rows are found in the Aare, archaeologists could reconstruct more precisely how the bridge connected to the road system of Salodurum.

For now, the discovery turns a long-standing assumption into archaeological fact. Solothurn was a guarded crossing point tied into the military and transport geography of the late Roman world.

Cantonal Archaeology Office of Solothurn

Cover Image Credit: A diver photographs the 1,700-year-old remains of the Roman bridge in the Aare River. Kantonsarchäologie Solothurn / Roman Sollberger