In the years leading up to the Civil War, the black abolitionist William Still offered shelter to hundreds of freedom seekers as they journeyed northward. His narrow house in Philadelphia served as an important stop on the Underground Railroad—and as Meagan Flynn reports for the Washington Post, a team of preservationists believe they have finally identified the home where Still and his wife Letitia once lived.

Earlier this month, the Philadelphia Historical Commission voted to include a row house on South Delhi Street (formerly Ronaldson Street) in the Philadelphia Register of Historic Places, which ensures that the property cannot be demolished or significantly altered. The house was remodeled in 1920, but experts say that the front marble steps appear to be the same ones that Still and many people escaping slavery would have stood on more than 150 years ago.

In their search for this important historic landmark, preservationists paged through many 19th-century maps and city records. Some of them identified the name of Still’s street, but did not specify the house number. Then one of the historians, Jim Duffin, came across an 1851 newspaper advertisement for a dressmaking business “done in the best manner by Letitia Still”—which included her address.