PITTSBURGH (AP) — Dozens of Civil War-era cannonballs unearthed at a Pittsburgh construction site will be removed by a Maryland firm.

The Pittsburgh Post-Gazette reports Ordnance Holdings Inc., of Reisterstown, has been hired to remove the cannonballs found near the former site of the Allegheny Arsenal. The arsenal supplied the Union Army, and an explosion there in September 1862 killed 78 people, many of them female employees.

Franjo Constructions, of Homestead, a Pittsburgh suburb, unearthed the cannonballs — believe to be 35 to 43 of them — during excavation for a planned apartment complex.

The public will not be allowed to watch their removal, for safety reasons.