Archeologists using laser technology have discovered a 2,000-year-old Roman military camp high in the Swiss Alps, uncovering a treasure trove of fortifications and artifacts, including arrowheads, slingshots and lead sling bullets bearing the stamp of the Roman 3rd Legion.

The site was found 2,200 metres up in the Colm la Runga corridor of Switzerland’s Oberhalbstein Alps near the Italian border.

The researchers from the University of Basel and the Archaeological Service of Graubünden were studying a nearby Roman-era battlefield when a volunteer discovered the encampment in images from airborne Light Detection and Ranging.

Known by its acronym LiDAR, the remote-sensing technique uses the reflected light from laser pulses to measure precise distances and create topographical maps. The data exposes anomalies, even subsurface ones, that may be manmade.

In this case, three ditches and a rampart stood out as the first evidence of the camp situated 900 metres above the battlefield where Roman legionaries and local Suanetes tribesmen fought in 15BC. The team has been studying the battle site since 2021.

The camp is located in a remote southeast corner of Switzerland on what would have been a strategic position on Colm la Runga, providing its occupants with a panoramic view of the surrounding valleys.

It was an ideal vantage point from which the Romans could monitor and control key mountain passes. The researchers say the site would have played a crucial role in their strategy to secure the Alps, essential to the security of northern Italy.

“The sensational discovery of a Roman military camp in Graubünden once again makes it clear that archaeological research into ‘Roman Switzerland’ continues to have great surprises in store,” said a translated statement from the Canton of Graubünden, the administrative region in which the sites are located.

“The discovery on the Colm la Runga is also outstanding because the advance of the Roman armed forces can now be precisely traced over several dozen kilometres.”

Evidence linking the encampment to the fighting is clear: the 3rd Legion was involved in the battle at nearby Crap-Ses and dating of the artifacts recovered from the site jibe with those found scattered across the battlefield.

Archeologists believe the site is linked to a known decree from Roman Emperor Augustus to bring the area under Roman control in 15BC.

Switzerland is dotted with columns, villas, amphitheatres and other remains of ancient settlements dating to Roman times. But no battlefields had been identified before the Crap-Ses site was discovered in the idyllic mountain meadow where researchers now believe the Roman occupation of Switzerland may have begun.

Swiss researchers believe a 2,000-strong taskforce of three military units—from the third, 10th and 12th Roman legions—clashed with 500-1,000 local fighters at the hilltop near the Crap-Ses gorge between the towns of Tiefencastel and Cunter.

Roman rule would gradually consolidate with the establishment of colonies, mostly in western Switzerland. Legionaries repeatedly advanced into the mountains through the first century BC to quell unrest, prevent raids and attacks on travellers, and secure a transit route to Germany.

In recent years, some 40 scientists along with students and volunteer detectorists have unearthed thousands of Roman military artifacts throughout the rolling meadow were the two sides fought. Among them: ancient swords, slingshot bullets, brooches, coins, shield fragments and several thousand Roman hobnails.

In the fall of 2023 alone, the researchers were finding 250-300 objects a day over a three-week dig. Crossbow bolts and the lozenge-shaped lead slingshot bullets provided insight about the legions and exactly where the clashes took place.

“This is the first time that remnants from a Roman battle site have been found in Switzerland,” project head Peter-Andrew Schwarz told SWI swissinfo.ch, the country’s international news service, in 2021.

“It seems that the Romans attacked their enemy on one side of the valley and then drove them over a river to the other side, before attacking again.”

While many details of the encounter are still unknown, the archeologists believe the Romans initially unleashed long-range weapons and slingshots on the Suanetes. The distribution of the bullets and their stamps over the 35,000-square-metre conflict site pinpoint the various battlefield positions.

About the size of a large olive, the slingshot bullets were deadly. Recent experiments have shown that, in the hands of a skilled fighter, the heavy lead or stone projectiles had stopping power approaching that of a present-day handgun.

But the most important finds are the hobnails, Schwarz has said.

Some 2,500 hobnails from Roman boots were left behind. The location of each hobnail marked where fighters stood or fell, helping chart the course of the battle.

The team also found fragments of swords and other weapons, but no human remains. The Romans and locals cremated the fallen.

This rich collection of archeological finds could well have remained hidden, even after several Roman artifacts were found on the steep meadow in the early-2000s. Once they were unearthed, the site was believed to have been picked clean.

That is until 2018, when a local amateur archeologist started finding Roman objects with his metal detector. His name was Lukas Schmid, a newly minted dentist, and he uncovered 250 pieces in three years, including a spectacular Roman dagger.

“The signal from the metal detector was very inconspicuous and quiet. At first there was nothing to suggest such a large find,” Schmid told SWI swissinfo.ch. “As I dug deeper, the tension rose—I knew it had to be an old object.

“When I exposed one end of the object, I saw that it was a dagger. When I saw it was a complete dagger, I was overjoyed. It’s fair to say that this is certainly my most spectacular find to date. But smaller finds—coins or fibulae [brooches]—can also be very important, as these are easy to date.”

The professionals moved in after the dagger turned up in 2021 but, as emphasized by the recent discovery of the encampment, amateurs remain a critical element of the project.

“Without detectorists like Lukas, we would have had no knowledge of this site,” said Schwarz, a University of Basel archeology professor. “He was the one to make the first important finds.”

The territory that makes up present-day Switzerland was part of the Roman Republic and Empire for about six centuries, beginning with the step-by-step conquest of the region by Roman armies from the 2nd century BC and ending with the Fall of the Western Roman Empire in the 5th century AD.

Area tribes were subjugated by successive Roman campaigns aimed at controlling the strategic routes from Italy across the Alps to the Rhine and into Gaul.

The Suanetes were among these alpine tribes, part of a confederation known as the Raeti, whose language and culture were related to those of the Etruscans.

Under the Pax Romana, the area was integrated into the thriving empire, and its population assimilated into the wider Gallo-Roman culture by the 2nd century AD. The Romans enlisted the native aristocracy in local government, built a network of roads connecting their newly established colonial cities, and portioned the area off among the Roman provinces.

Roman civilization began to withdraw from Swiss territory in the 3rd century AD. But Roman control did not disappear until the mid-5th century, after which Germanic peoples began to occupy the region.