Three hand-drawn maps set up in his living room depict Pennsylvania, Franklin County, Pa., and Washington County.
There are 53 marked Underground Railroad stopover sites on the Pennsylvania map. Franklin County, with six marked sites, is second only to Philadelphia - which was a nerve center for the Underground Railroad - with 15.
Putting the web together
Washington County has five known Underground Railroad paths running through it, but has no marked stopovers on Gerhart's map.
"This is a web, and what you're trying to do is put the web together," Gerhart said. "I'm going to have to be a super history detective to get it in Washington County, but I'll get it."
Gerhart and Ted Alexander, chief historian at Antietam National Battlefield, said fugitive slave laws - statutes passed by the U.S. Congress in 1793 and 1850 to provide for the return of slaves - made it illegal to harbor a slave, and, in Maryland, secrets about doing so were kept well.
"Three generations occurred between the Civil War and myself," Gerhart said. "Those generations buried everything."
In addition to the five documented routes through Washington County, there are rumored stopover sites in the county, but that doesn't satisfy Gerhart.
"I don't do stories and I don't do hearsay," he said.
Alexander said one route took escaped slaves from Boonsboro to Smithsburg to Waynesboro, Pa. Another route took them from Hancock to Mercersburg, Pa., along the Tuscarora Ridge on Cove Mountain, he said.
"Mercersburg is a key Underground Railroad site in the 1840s and 1850s," Alexander said.
There was a Berkeley Springs, W.Va.-to-Pennsylvania route, a Rouzerville, Pa., route, and a Hagerstown-to-Chambersburg, Pa. route, he said.
Hagerstown was nicknamed "Little Virginia" during the height of slavery because it held "one of the most punitive slave auctions," and was in frequent communication with Virginia slaveholders, Gerhart said.
Slaves were held in the old Washington County Jail, in the historically black Jonathan Street neighborhood, which was up the street from the auction block. The auctions were held at what now is the site of the Washington County Courthouse. The jail was torn down in 1985.
Alexander said that in 1790, Maryland was home to 319,728 people. Of those, 208,649 were white and 111,079 were black. Of the black population, only 8,043 were free.
Alexander said slavery in Maryland hit its peak in 1810, when the number of slaves was recorded at 115,056.
By 1850, the number of enslaved blacks had decreased to 90,368, while the number of free blacks increased to 74,723, Alexander said.
"What's going on is this: The slave population is declining and the free population is increasing," he said. "With Maryland's proximity to the Mason-Dixon Line, some of those slaves were escaping to the north."
Road to freedom
Washington County was home to James W.C. Pennington, who escaped from Rockland, a plantation in the Tilghmanton area. He eventually became an abolitionist spokesman, said Edie Wallace, a local historian who works for Paula S. Reed and Associates Inc., an architectural history group.
Pennington walked along the National Road - now U.S. 40 - and hid beneath bridges and corn shocks to escape detection before he nearly reached Reisterstown, Md., according to "Underground Railroad in Delaware, Maryland and West Virginia," written by William J. Switala.
Pennington was caught before he reached the Mason-Dixon Line after changing course north, but he eventually escaped from his captors and attained his goal of freedom, according to William Still's "The Underground Rail Road: A Record," published in 1872.
Pennington arrived at the home of William Wright, a Quaker abolitionist, who was living near the foot of the southern slope of South Mountain in Adams County, Pa.
Pennington learned to read and write there, and later obtained an education at Yale College while working as a janitor, according to the book.
Wright assisted thousands of escaped slaves, according to Still's book.