Rock and roll

SIR – With regard to your report (December 30), “Catapult stone found at Edinburgh Castle”, may I suggest a different use for the stone ball?

There was no requirement for trebuchet projectiles to be streamlined, or even round. Any rough rock that could sit in the sling would do the job.

However, stones were chiselled into a ball shape for use as “rolling stones”. Defenders holding the high ground used these stones (probably carved by captured enemy soldiers) to roll down the slopes against a besieging enemy.

They could be used night and day, and could be guaranteed to wreck an enemy camp built too close, or to scatter advancing troops. E C Coleman

Bishop Norton, Lincolnshire