Crews begin removing more than 300 Civil War-era cannonballs in Pa.

More than 300 Civil War-era cannonballs were unearthed at a construction site near Pittsburgh in late March 2017.

CBS Pittsburgh

PITTSBURGH -- Construction crews began Wednesday removing more than 300 Civil War-era cannonballs found underground a construction site in central Pennsylvania.

The hundreds of cannonballs buried underground are a stark reminder of history, but when they show up during excavation for new apartments, that's a little different, CBS Pittsburgh reports.

Crews initially found a few of the black powder filled cannonballs, but that quickly changed to more than 300.

It's a delicate process that will take several says.

"Even though these things are 200-plus years old, we are using safety precautions," said Nick Leonello, of Franjo Construction.

The cannonballs were found in Lawrenceville last month and they are believed to be pre-Civil War.

Contractors happened upon them while digging up the site, and now they have to safely dispose them.

"There is black powder in these cannonballs, and black powder is a very dangerous substance. Even after it gets wet, when it dries out, it can still be dangerous," said Leonello.

Crews have brought in dumpsters filled with foam to put the cannonballs into once they are removed from the ground.

Right now, it isn't clear if they will be disposed of at the site or moved to another location. The current challenge is to keep digging until they have found all the cannonballs that have been buried.

"We aren't allowed to stop until we don't see anymore. As long as there are more cannonballs in the hole, the specialty contractor has to excavate," Leonello said.

All of the cannonballs that have been located are currently being stored on sight. Once contractors know how many they have, they can determine how they will get the rid of them.