One of Baltimore's hoariest legends has been verified with the discovery of more than 200 feet of white-walled tunnels under Federal Hill's north slope facing the Inner Harbor.
Early in June construction workers located the entrance to a 19th century commercial sand mine, a multichambered vein under the park's slope. Researchers speculate that the sand was quarried for use in the manufacture of high-quality glassware.
The presence of the tunnels was kept confidential, however. Community leaders were not notified, and since their discovery, the entrances have been covered over with sandbags and dirt, again making them inaccessible.
For decades the sides of Federal Hill have been falling in after rain and snow storms. Neighborhood hearsay blamed the cave-ins on a network of "secret" tunnels supposedly used during the Civil War, possibly linking a fort there with Camden Station. Other stories said the hill was laced with iron ore or with clay mines. One version said ancient brewers dug caverns there to cool beer.
The truth turned out to be no less intriguing than the rumors, said Louise F. Akerson, archaeological curator for the Baltimore City Life Museums.
"It's absolutely wonderful," she said. "The sand was very white and fine. Workers used hand picks to get it out."
"It's like a tomb in there," said Dan Deitrich, a city inspector who was on a job site when the underground chambers and corridors were initially discovered June 3.
The presence of the tunnels was not initially announced, to keep curious souvenir hunters out. The entrance to the tunnel was sealed about five weeks ago, but the main tunnel was left undisturbed within the hill itself.
Workers located a narrow entrance about halfway up the hill, 165 feet east of the Battery Avenue side of the park. Earlier in the spring, the city had begun a $900,000 drainage control and stabilization project designed to halt the hillside's frequent cave-ins and erosion, a condition that has plagued Federal Hill for years.
"The sand down there was fine and glassy, full of mica," said Dan Ogle, superintendent for Potts and Callahan, the construction firm fixing the hillside. "The walls were tight and solid.
"The temperature was about 50 degrees. The entrance was narrow, but once you got down there and walked around, you could see it was built to last," Mr. Ogle said. "We even found the places on the wall where they put candles. The fire smudges were still on the wall."
He said the mine was about 12 feet high and had several branches, including the "big room" -- a chamber nearly 55 feet long, 15 feet wide and 12 feet high -- where large amounts of sand were once dug. The arched tunnels, wide and tall enough for several workers, stand 20 to 30 feet below the surface of the top of Federal Hill Park.
Photographs Mr. Ogle made of the site show that someone had carved the name "Zimmerman" into the hardened sand wall. Under it was written "Balto."
There were other examples of 19th century graffiti, but the letters were difficult to read.
Archaeologists also located a shard of a ceramic pitcher or vase, which they said dated from the middle of the 19th century. There was no evidence of Civil War materials.
Because of this shortage of evidence, it is not known exactly when the tunnels were built, nor is it known how long they had been sealed.
Once the tunnels were discovered, construction crews stopped work so archaeologists could study the site. The decision was made to leave the mine as it was, except for its entrance nearest the hill's slope. Construction workers sealed two entrances to legs of the mine with 2,800 sand bags.
"We kept it all quiet because I have enough trouble keeping the kids out," Mr. Ogle said.
"I didn't want people running around with picks and shovels. Every day I'm chasing people with metal detectors away."
Ms. Akerson, the city's archaeologist, agreed with the decision to close the entrances.
"The mine is unique to Baltimore and maybe to the region. It made for the best of all worlds to seal it off and preserve it for the future," she said.
Local historical researcher Barbara Weeks expressed surprise at the tunnel's discovery.
"The massive amount of shoring-up along the north slope over the years seemed like it would have wiped out anything like this," she said.
A report she prepared of the area says there was a famous glass blower, Frederick Amelung, who worked near the base of Federal Hill in the late 18th and early 19th centuries. She also identified a German immigrant, Ferdinand Kopp, as someone who had a sand operation in the area.
"I can't say I'm surprised. We've heard about the tunnels for years. Some of my family worked in the sand mines years ago," said Patrick Frazier, a resident of the 300 block of E. Hamburg St. and a neighborhood historian of Federal Hill.
Federal Hill was named for Maryland's ratification of the Constitution and for a large parade and party staged there May 1, 1788. During the Civil War, Union troops occupied the hill and built a fort. After the war, battlements were removed and it was converted into the present park.
Before that, Baltimore shipping merchants maintained an observatory there.