Judith Hernstadt bought the drawing from an antique dealer more than 40 years ago and paid less than $1,000.
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Being a collector, she knew it was special, but had not idea just how rare.
"It had an energy to it, was fairly detailed, in terms of what it did have of several figures in the wagon and what it said on it was exciting to me," she said.
In faint writing, the sketch is said to be soldiers from the North Carolina Brigade of the Continental Army marching through Philadelphia.
Matthew Skic is a curator at Philadelphia's Museum of The American Revolution.
"She showed it to me and my jaw dropped," Skic said. "I recognized the details in this sketch almost immediately and realized its historical significance."
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He took the work back to Philadelphia and carefully examined it and learned it was authentic, created in 1777, by Swiss artist Pierre Eugene du Simitiere.
It's the first wartime depiction of the brigade and only second-known depiction of female camp followers.
"The historical value of this piece is through the roof," Skic said.
Hernstadt donated the piece to the museum to share her treasured gem with the world.
"Hopefully more people will appreciate the excitement of collecting, studying and doing research and go to museums more," she said.
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