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‘Secret’ tunnels are hidden under Baltimore’s Federal Hill. Where did they come from and what lies inside?

While Federal Hill’s panoramic view of downtown Baltimore makes it a favorite destination for tourists and neighbors alike, its frequent cave-ins and landslides have long inspired questions and myths about a network of “secret tunnels” below. (Ulysses Muñoz, Colin Campbell / Baltimore Sun video)

Editor’s note: This is the latest in a series of occasional articles inspired by readers' curiosity. What do you wonder about the Baltimore area that you'd like us to investigate? Tell us at baltimoresun.com/ask.

While Federal Hill’s panoramic view of downtown Baltimore makes it a favorite destination for tourists and neighbors alike, its frequent cave-ins and landslides have long inspired questions and myths about a network of “secret tunnels” below.

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It’s true that large mines and other tunnels were dug into the hill more than a century ago. Some of the underground passageways have been verified by archaeologists and sealed with sandbags to keep out amateur explorers, out of safety concerns. Many others have caved in or been filled in by the city.

But who built them? Why? And why are Baltimoreans so fascinated by their lore?

“The idea of a catacomb you would go down into, [that] only you would know about ... digging into the depths of the hill, finding its inner secrets,” said David Gleason, president of the Society for the Preservation of Federal Hill and Fell’s Point, “it’s a romantic idea, sort of like ‘Raiders of the Lost Ark.’”

The Baltimore Sun investigated the origin and uses of Federal Hill’s tunnel network by reviewing historical documents and news accounts, and interviewing nearby neighbors, contractors who have worked on the hill, and an archaeologist who explored some of them in the early 1990s.

‘A series of shafts and off-shoots’

Federal Hill long served as a repository of sand, clay, silica and iron ore, and industrial mine shafts and tunnels pockmarked the hill for years before the city designated it as a park in 1880, according to “Baltimore Subterranean,” a 1954 report by researcher George Wetzel.

Shaum Glass Works, a company once headquartered on the north side of the hill, used the sand for glassmaking — one of several industries that drew materials both from the hill’s surface and from underground, the researcher wrote, citing an 1846 article in The Sun.

“So extensive were the mining excavations under the Hill, that in Feb. 1840 it was feared the Hill would be dug down before a park could be established there,” Wetzel wrote.

Louise F. Akerson has personally explored the hill’s belly.

The former archaeological curator for the Baltimore City Life Museums ventured into a 19th-century commercial sand mine in July 1992, after construction workers shoring up the north side of the hill discovered a void in the hill that turned out to be the mine’s entrance — leading to some cavernous rooms as much as 11 feet high.

“The tunnel was divided into a series of shafts and off-shoots of varying heights,” she wrote afterward in an article for the Journal of the Archaeological Society of Maryland.

Digging into the depths of the hill, finding its inner secrets. It's a romantic idea, sort of like 'Raiders of the Lost Ark.'


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In the depths of the hill, Akerson and the construction workers who discovered the tunnel unearthed a trove of artifacts, including a wooden pipe, a pocket knife and wick material, a piece of a chamber pot, a fully intact beer bottle, and “a shard of Rockingham glazed ceramic which was probably manufactured in Baltimore by the Bennett Pottery Company around 1850,” Akerson wrote.

Their most fascinating finding was a name, “Zimmerman,” hand-carved into the wall of a tunnel, with “Balto” scrawled underneath it. Other names on the wall had faded and could not be read clearly.

Federal Hill is a prime spot to take in Baltimore's skyline.
Federal Hill is a prime spot to take in Baltimore's skyline. (Algerina Perna / Baltimore Sun)

There was still soot on the walls above the mine’s old candle notches.

More than 25 years later, the archaeologist remembers being awestruck by the various artifacts.

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“Just imagine the person who made it or handled it,” she said in an interview. “It just boggles the mind. Seeing the initials on the wall was the same feeling. This is somebody who lived 100 years ago that put their initials in the sand.”

A military ‘escape route’?

At least one theory surrounding Federal Hill’s tunnels is steeped in Baltimore’s wartime history.

After a major cave-in of Clement Street renewed public interest in the tunnels in 1951, Donald Stewart, who lived on Warren Avenue, spread the legend: Military tunnels built between Federal Hill and Camden Station during the War of 1812 had been discovered, enlarged and reinforced by Union soldiers occupying the hill during the Civil War five decades later, he said.

“The Union Army rebuilt the tunnels for troops to march through from their trains at Camden Station to either Federal Hill or to boats, and they were used largely by wounded soldiers and others coming from the South," Stewart told The Baltimore Sun in an interview at the time.

A cannon is trained on Baltimore's central business district after Union troops occupied Federal Hill under the command of General Benjamin F. Butler following the riots of 1861.
A cannon is trained on Baltimore's central business district after Union troops occupied Federal Hill under the command of General Benjamin F. Butler following the riots of 1861. (Baltimore Sun file)

The existence of such a tunnel has never been verified.

But Union troops did discover the mines during their occupation, the researcher Wetzel wrote, citing the autobiography of the fort’s commander, Gen. Benjamin Butler. A Union captain who found a tunnel on the night Butler arrived in Baltimore in May 1861 breathlessly reported it to the general, anxious it had been dug by infiltrating Confederates seeking to blow up their fort on the hill.

“Together they entered it and found only the tools of a sand miner,” Wetzel wrote.

An old cannon was found in a network of underground rooms at the northwest corner of the hill during a sewer project in the 1900s. But Wetzel — skeptical about the tunnels’ military origin — concluded that it had most likely toppled from its bastion atop the hill during an 1864 landslide into an existing sand mine below.

Jim Hall, a former city planner who lives on Grindall Street, is certain the Union forces dug at least one military tunnel. He said the two houses next door to his collapsed into it sometime in the 19th century.

Much of that tunnel has been filled by the city after many cave-ins over the years, but it once ran from Federal Hill toward where Digital Harbor High School now stands, Hall said.

“This is a tunnel. This isn’t a mine,” Hall said. “This is getting somebody somewhere. Now, why? … It would have been very important to the military to have an escape route.”

Bill Houck, part of an Allied Contractors crew shoring up the eastern side of the hill last month, said he had found military artifacts and other items inside the hill during a utility project on its north side in the 1970s.

“We found some musket balls, a rusted-up gun and some other relics, pottery and things like that,” Houck said.

‘The beer ... was still quite good’

Two boys exploring the tunnels in 1856 confirmed another piece of the lore: that brewers found and used the cool, dark underground passages as vaults to store their beer.

The young explorers stumbled upon a cache of lager kegs that had been stored there two years earlier and abandoned after a landslide buried them, according to Wetzel’s research.

“The beer in the kegs was still quite good,” he wrote, “as attested by the boys, who sampled most of it.”

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Barbara Weeks doesn’t have high hopes for any such discoveries today.

Weeks, a local historian formerly with the Maryland Historical Society, expects many, if not most, of the tunnels have caved in or been filled over centuries of shoring the hill’s sides.

“Having read the parks department’s annual reports throughout the 19th century and into the 20th century, where the collapse of the tunnels was repeated and the repair and shoring up of the tunnels occurred frequently, I concluded that there would be very little left of these tunnels,” Weeks said in an interview.

But Rebecca Alban Hoffberger, founder and curator of the American Visionary Art Museum at the eastern base of the hill, warned officials this month not to build a proposed staircase on the eastern hillside without checking for tunnels.

“If I get overruled, and you build this thing, I'm telling you, do ground-penetrating radar,” she said, “because I think you're going to have to do a hell of a lot more of steel structure to support the weight.”

A portion of Federal Hill near the American Visionary Art Museum slid into the street in December.
A portion of Federal Hill near the American Visionary Art Museum slid into the street in December. (Jerry Jackson/Baltimore Sun)
‘The stuff of legend’

The mystery of the unknown and romantic notions of urban archaeology stoke Baltimoreans’ perpetual interest in the tunnels, said Gleason, the preservation society president.

Unlike the far larger Howard Street and Baltimore & Potomac train tunnels under the city, the passages within Federal Hill are “the stuff of legend,” he said. “That’s part of the attraction.”

An underground parking garage proposed inside Federal Hill at one point was a non-starter, said Sandy Apgar, chair emeritus of the South Harbor Renaissance, a nonprofit that helps preserve and improve Federal Hill.

Apgar, who has lived on Warren Avenue for nine years, envisions a more exciting way to transform the inside of the hill: fortifying the tunnels and opening them for tours, “as a small urban equivalent of Luray Caverns.”

“Some of us would like to see access to them,” he said. “Why not? We're always looking, obviously, for revenue-generating opportunities, because the support to do what we've done is mainly private.”

The notion of an adventure inside one of Baltimore’s most historic landmarks would be a strong draw, Apgar said.

“The tunnels have their own magic,” he said.

Baltimore Sun researcher Paul McCardell and reporter Jacques Kelly contributed to this article.

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