On Monday, construction workers digging at the site of the former Suit Corner store on the southwest corner of Third and Market Streets uncovered something other than a blazer and trousers.

Specifically, construction worker Ery Chacon said Tuesday, they found two brick arches about 10 feet below street level - and experts say they could be from before the nation was founded.

As it happens, people who were collared ended up at that location long before it became the Suit Corner, which was destroyed by fire in 2014. A jail stood there for much of the 18th century.

Part of the site, including one arch, is the property of former Suit Corner owner Jerry Ginsberg, who hopes to reopen the store there. A West Virginia company owns a portion of the property that includes the other arch.

A 1918 book, Market Street Philadelphia by Joseph Jackson, says the jail was built in 1722 to replace a prison nearby. Later, a jail was built on the southeast corner of Sixth and Walnut Streets, but it was used during the Revolutionary War for prisoners of war.

"Consequently it was not until the war for independence was concluded that the prisoners were removed from Third and Market streets to the new jail," Jackson wrote. "This was accomplished in 1784, and the old structure soon gave way to modern buildings for dwellings and stores."

Philadelphia historians are not certain that the arches are related to the jail, but records point to the site's rich history.

The Philadelphia Historical Commission was aware of the arches - also called vaults - before the digging began, executive director Jonathan Farnham said in an email.

An undated and unsigned note in the commission's file on 300 Market St. "notes that the Historical Commission was aware of the brick vaults in the basement and believed that they 'could be remains of the city jail - altho vaults clearly had commercial uses,' " Farnham wrote.

Farnham cautioned, however: "Given that the jail and workhouse were apparently stone, not brick, and the surviving vaults are brick, I would suggest that the vaults probably date to the 1785 house, or were added later when the building was apparently converted to commercial use. Vaults under sidewalks are very common features of Old City commercial buildings."

According to Jackson's book, the jail consisted of a pair of two-story buildings: a debtor's jail facing Market (then known as High) Street, and a structure facing Third Street that served as a workhouse for prisoners. The hewed stone buildings were joined by a wall, he wrote.

Archaeologist Jed Levin, a member of the Philadelphia Archaeological Forum, said the openings might have been used for storage of coal, wood, or wine. It was common to have vaults in the 18th and 19th centuries for that purpose, he said. These may have belonged to a residence or stores that occupied the space after 1785, he said.

Farnham wrote that a 3½-story building was built there for residential use in 1785, and later was expanded to 4½ stories. Several stores occupied the space in 1801, "including a paper store, merchant, leather dresser, breeches maker & glover, hardware merchant, and watchmaker & jeweler," he added. After 1916, all but the first floor was removed, but the ground floor survived until the fire in 2014, Farnham wrote.

Levin said he wished that archaeologists could visit such sites before construction.

"Each time this happens, I'm left wondering what we might have learned if we had taken a little time," he said.

Chacon, the worker at the site Tuesday afternoon, said that he works for Frankford concrete contractor P. Santos Co., and that his supervisor had told workers to dig away from the brick structures after they uncovered them.

The Suit Corner, and the Shirt Corner on the northeast side of the block, were owned by brothers. The latter was converted into a CVS store and apartments last year.

Ginsberg, 75, the Suit Corner man, said he knew about the brick arches all along.

"It was one of the best-kept secrets I remember," he said. He said electricians and city inspectors occasionally would go down to the basement, where the arches were in plain view, but he decided not to ask about them for fear of having to give up his location for historic preservation. "If they're not going to make a big stink about it, I'm not going to say anything," he said.

He'd taken a few steps inside once, before friends scolded that the bricks could collapse on him. For much of his time there, he had boarded up the arches with plywood.

"I knew Pandora's box would open eventually," he said.

Now, his son Gary and daughter Stacey run Shirt Corner Plus, at 630 Market St.

It's not on a corner.

lfeiner@philly.com / 215-854-5915 / @lauren_feiner

Staff Writer Dylan Purcell contributed to this story.