PHILADELPHIA — Archaeologists and park officials held a ceremony Tuesday to commemorate the end of a dig that exposed evidence of where George Washington kept his slaves while he was president.

The archaeologists discovered remnants of a hidden passageway used by the slaves in what is now called the President's House, a spot that is just steps from the Liberty Bell and Independence Hall. Washington lived at the house while he was president in the 1790s, when Philadelphia was the nation's capital.

The underground passageway, which is a few feet from the Liberty Bell Center, was designed so Washington's guests wouldn't see his nine slaves as they slipped in and out of the house.

"It's the only place in America where black slavery and white freedom literally stand side-by-side — mere inches away from each other," said Michael Coard, an attorney who leads a group that worked to have slavery recognized at the site.

The archaeological dig was begun as a prelude to a new exhibit about the President's House. The original plans called for filling in the ruins of the house and building an abstract display and exhibit.

But the discovery of the slave passage prompted city and park officials to change course. The new site will incorporate the archaeological findings into the exhibits, said Emanuel Kelly, principal of the design firm working on the project.

An oversight committee is considering four different options to highlight the dig's findings, Kelly said. One possibility is to cover the area with glass so visitors can look down at the ruins. Other options involve developing a tunnel or partial basement to allow people to be at eye level with the findings.

In addition to the passageway, archaeologists found the remains of a basement that was never noted in historical records, and a bow window that was the architectural precursor to the Oval Office.

"Many of us on the archaeological team are still shaking our heads in amazement," said Jed Levin, an archaeologist with the National Park Service.

Officials temporarily closed the site Tuesday to shield it from the weather and elements that could cause the ruins to deteriorate. They plan to cover the ruins until the memorial design is finished and construction begins.

Park officials estimated that 250,000 people visited the dig in the four months since it opened. More than 100 people attended the closing ceremony — many of them crowded onto a small wooden platform overlooking the ruins.

Officials ended the ceremony by putting remnants of slave history into the dig: water from the Nile River, sand from the Nile's banks and small plaques with the names of Washington's slaves.

"I know many people will be aghast that we can talk about George Washington the slaveholder and George Washington the president in the same breath," said Cheryl LaRoche, a cultural heritage specialist.