Archeologists have found what they say are 16th century time bombs.

Honam Cultural Property Research Center said Thursday that eleven devices were found at an ancient fortress site in Gochang, North Jeolla Province.  

Known as "Bi-geok-jin-cheon-ryoe" in Korean, the weapons are cast iron spheres containing gunpowder, pieces of metal and a timer device. 

Cannons would fire the sphere, and it would explode after a designated time interval.

The weapon is believed to have been invented by artillery master Lee Jang-son during the reign of King Seonjo shortly before a 1592 invasion of Korea by Japan.