Forgotten Tunnel Found Beneath Danish Train Station

Wood used to build the secret passageway came from a tree felled in 1874, according to a new analysis

Remains of secret tunnel in Copenhagen
Archaeologists are unsure of the long-forgotten passageway's purpose. Courtesy of the Museum of Copenhagen

Archaeologists conducting excavations at a train station in Copenhagen, Denmark, have unearthed a mysterious tunnel dating back to the 1800s, reports Kasper Bruun Vindum Brandt for Danish broadcast station TV2 Lorry.

Found some 19 feet below Østerport Station, according to the Copenhagen Post, the wood-lined passageway is now under investigation by researchers at the Museum of Copenhagen.

“When you find such a tunnel, it gives a rush to the body,” archaeologist Christian Andreas Flensborg tells TV2 Lorry. “ ... You ask yourself how extensive these systems are and are there many more tunnels.”

So far, excavations have revealed almost ten feet of the narrow tunnel—and researchers think it could keep going.

Says Flensborg, “The tunnel is seemingly cut off by the rampart at Østerport Station, but the other end continues under Østbanegade,” a street running north of the Copenhagen station.

“We don’t know if it turns or where it ends,” the archaeologist adds. “It’s a mystery.”

The square tunnel is just over three feet wide and three feet tall, making it a tight squeeze likely reserved for emergency escape rather than daily use. It passes beneath what used to be Copenhagen’s ramparts, or defensive walls, lending support to the idea that it may have been used as an escape route.

Per Encyclopedia Britannica, Bishop Absalon of Roskilde fortified what would later become the Danish capital with ramparts and a moat in 1167. A series of armed conflicts—including the destruction of buildings during the Protestant Reformation, a two-year siege by Sweden in the 17th century and bombardment by Britain in the early 19th century—offered ample justification for the city’s militarized exterior. In 1856, however, the defensive measures were torn down to allow for expansion of the growing urban center.

Based on the tunnel’s location in relation to the historic fortifications, the archaeologists initially theorized that it dated to the 17th century. But an analysis of the wood used to build the structure showed it came from a tree felled in 1874.

The passage’s construction methods are similar to those seen in tunnels dug on the Western Front of World War I, Hanna Dahlström of the Copenhagen Museum tells TV2 Lorry. She notes that the tunnel’s relatively recent wood may date to repairs made centuries after its initial construction.

According to TV2 Lorry, the find has left archaeologists wondering if other tunnels snake below Copenhagen’s streets. The museum notes that no other tunnels of this kind have been found in the city before; interestingly, the newly discovered passage doesn’t appear on any of the maps or historical documents consulted by the museum.

“It’s odd that you make a tunnel that no one knows about,” says Flensborg. “This construction must have been secret. It’s a part of Copenhagen’s military history.”

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