PETERSBURG, Va. (WRIC) – Police are guarding a Civil War museum in Petersburg, Virginia, after a bomb squad verified some of the antique ammunition inside still contains live explosives.

The museum had been closed for the last 18 months. Tuesday afternoon, people working to re-open the museum found several dozen cannon balls in storage.

A Virginia State Police bomb squad determined that at least three of the cannon balls are active.

A number of types of artillery ammunition used during the Civil War included explosives inside of spherical iron casings, according to the National Park Service.

The live projectiles are believed to have been in the museum for about 70 years.

According to a city official, a bomb disposal team has been called to retrieve the ammunition.

The Siege Museum commemorates the grinding siege that Union troops carried out against the key Confederate railroad hub during the Civil War.