Sling bullets, used by Roman soldiers in an attack on a fort in Scotland some 1800 years ago, appear designed to whistle in flight. A battery of them could be terrifying; or perhaps simply very loud and annoying.
These holes converted the bullets into a "terror weapon," said archaeologist John Reid of the Trimontium Trust, a Scottish historical society directing the first major archaeological investigation in 50 years of the Burnswark Hill site.
"You don't just have these silent but deadly bullets flying over; you've got a sound effect coming off them that would keep the defenders' heads down," Reid told Live Science. "Every army likes an edge over its opponents, so this was an ingenious edge on the permutation of sling bullets."
Archeology.co.uk conducted tests with replicas to see what it would have sounded like:
Two extraordinary facts concerning the small bullets with holes (now dubbed type IIIs) also emerged. First, they could be successfully slung in small groups of three or four to create a form of grapeshot. This had been independently confirmed by T Richardson in his work on Roman sling-bullets at the Royal Armouries. Even more intriguingly, the mysterious holes proved to confer an aerophonic quality: in flight, these lead shot whistled, or more accurately gave off a mechanical buzzing sound eerily reminiscent of an agitated wasp (click below to hear for yourself). Remarkable as it sounds, the simplest explanation for this design modification is that it represents an early form of psychological warfare. To put it another way, the Roman attackers valued the terror that hearing the incoming bullets would instil in the defenders.