Cannonballs halt construx

The discovery of a cache of cannonballs left behind after the worst civilian disaster of the US Civil War brought construction on a Pittsburgh apartment complex to a halt Tuesday while workers waited for the ordnance to be removed.

At least 20 cannonballs were unearthed Monday by a contractor on the site of the former Allegheny Arsenal, where a Sept. 17, 1862, explosion killed 70 mostly teenage workers.

Officials believe the cannonballs are stable, but have posted a 24-hour police guard on the site, according to a spokeswoman for the Pittsburgh Department of Public Safety.

Workers had been alerted to the danger and stopped when the first cannonball turned up.