|Date||12 February 2011|
|Location||Gefnan, Mynydd Llandegai||SH 61096 65123; 53.16504°N, 4.07924°W|
A rock cannon was a traditional pyrotechnic device fired to mark special occasions and celebrations.
It comprised a boulder into which a number of holes had been drilled. Each hole was normally around an inch across by five or six deep, and was linked to a neighbouring one via a shallow channel cut into the surface of the rock. Before firing, the holes were filled with black powder and packed with crushed rock. A black powder-filled goose quill served as a fuse and more black powder was laid in the grooves between the holes. The sights and sounds of a cannon in operation are said to have been rather marvellous.
There are over 200 known rock cannon sites in the slate quarrying areas of Gwynedd.