How train tunnels beneath Amsterdam revealed a medieval treasure trove

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How train tunnels beneath Amsterdam revealed a medieval treasure trove

Building Amsterdam’s North-South metro line was big trouble – a budget-blowing 15-year operation that involved carefully burrowing beneath the foundations of centuries-old architecture.

For archaeologists tasked with sifting through soft mud to preserve any history disturbed by the massive engineering project, it was no easy feat either. Their potentially hazardous work took place inside concrete boxes pressurized to keep out deluges from the Dutch capital’s ubiquitous waterways.

Today, the fruits of their subterranean labors can be seen at Rokin station, one of eight stops on the route and one that doubles up as an impressive underground archaeological museum, with nearly 10,000 artifacts on display.

The station, well worth visiting in its own right, is a testament not only to the rich heritage on which Amsterdam is built, but also to the engineers and archeologists who worked so hard to preserve it.

The fruits of their labor are displayed in two glass cases positioned between the escalators, one case at either end of the station. On any given day, it’s not unusual to find a commuter going up and down the escalators, just to get a better look.

Waterways tend to become dumping grounds, accumulating objects over the centuries. The Amstel riverbed around Rokin was no different.

“The sheer mass of material we unearthed during the construction of the North-South line was extraordinary,” says Peter Kranendonk, one of two senior archaeologists leading the excavations during the metro project.

“The construction gave us a unique opportunity to excavate under the city up to a depth of 30 meters,” he adds. The oldest items found were mollusc shells dating to over 115,000 years ago.

The artifact displays at Rokin station are organized into various themes. In the north display, the focus is on objects related to food, science and technology, arms and armor, communication, games and recreation, personal artifacts and clothing; while the south display includes items from buildings and structures, interiors and accessories, transport, as well as craft and industry. All of these artifacts provide insights into Amsterdam’s glorious, and sometimes unknown past.

“Some objects, like the 500-year-old coins, have a direct story behind them,” says Kranendonk. “On the basis of the finds, we can also say something about the use of an area,” he adds.

Under pressure

In one spot at Rokin, unearthing a concentration of chopped animal bones pointed to the existence of a butchery nearby in the 17th and 18th century. At another spot, an abundance of furniture fittings confirmed the presence of a furniture maker’s shop in the 19th century.

“Prior to the excavation of these artifacts, the city had an archaeological archive of only about 70,000 artifacts,” says Hoite Detmar, who served as the director of the North-South metro project from 2016 till its completion. “We found 10 times as many during the construction of the North-South line.”

Kranendonk elaborates on the rather unconventional excavation process behind these finds.

“This was not a normal dig,” he says. “Usually, excavation is done before building. But in this case, the construction plans were already finalized. So we had to become part of the existing process. The civil engineering team were building and we were excavating.”

For the archaeology team, working in the caissons was a novel experience. A caisson is a large watertight concrete chamber, open at the bottom, from which water is kept out by air pressure and in which construction work is carried out underground or underwater.

“It was an interesting experience but also a bit frightening,” says Kranendonk. “The deeper you go, the more compressed the air gets. It’s like deep sea diving,” To acclimatize to the caissons, teams had to spend time in a pressure chamber before entering and after exiting, otherwise they’d face risk of “the bends,” when gas bubbles form in the body, potentially leading to paralysis.

To enable people to engage with the Rokin displays at leisure, an online database of nearly 20,000 objects, Below the Surface, was created, providing information about every single item in the glass cases. “It’s a process of discovery in its own way,” says Kranendonk.

A documentary about the excavation called “Amstel, Spiegel van de Stad” (Amstel, Mirror of the City) and a beautiful coffee-table book, “Amsterdam Stuff” were also created.

“We knew we would be working in the city for a very long time and would inconvenience citizens a lot,” says Hoite Detmar. “This was one of the many ways we gave back to the city.”

In addition to the two archaeological displays, the walls of Rokin station adjacent to the tracks are covered with stone mosaics by artists Daniel Dewar and Grégory Gicquel depicting 33 of the artifacts unearthed – a keyboard, a pike, a teapot, dice, a butterfly, among others.

There is even a mosaic of a crocodile which represents a crocodile jaw that was unearthed, a rather unusual find for this part of the world.

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