Seven graves, probably dating back more than a century, were discovered under a house being renovated in the Fairmount section of the city, authorities said.

The shallow graves were revealed around 1 p.m. Saturday after a contractor gutting a three-story rowhouse in the 800 block of North 20th Street began to dig under the basement, police said.

The Medical Examiner's Office processed the scene, where bones from some of the graves were recovered, police said. The bones were quickly determined to be very old and were turned over to an archaeologist.

"The archaeologist will now do scientific tests to further this investigation," said police spokesman Lt. Frank Vanore. "I'm told the bones may have been there over 100 years."

Not all the bones, however, were preserved, police said. Many apparently were hauled away with buckets of dirt before the workers realized what they had uncovered.

The property is owned by Big Rental Inc. of Huntingdon Valley, records show. The company did not immediately respond to a request for comment.

Gwendolyn Brown, 52, grew up in the brick rowhouse and now lives next door.

"Me not knowing and growing up here, it was like a shocker," Brown said yesterday, recalling her reaction when police told her what they had found.

Brown and a brother inherited the house after their mother, Katherine Irby, 76, died in 2005, she said. They sold it soon afterward.

Irby had lived in the house with her husband, Joenathan, since 1951, records show. Joenathan Irby died in 2002.

Brown's husband, Cedric, 49, said crews had been gutting the house for several weeks and on Thursday began to break into the concrete basement floor.

On Saturday, police showed up and guarded the house into the night, he said.

Cedric Brown speculated that perhaps the house was built on an old cemetery.

"I'm quite sure the mystery will be solved at some point in time," he said.

Contact staff writer Robert Moran at 215-854-5983 or bmoran@phillynews.com.