When archaeologists recently uncovered bullets from a Roman battle site in Scotland, they noticed something unusual about them: They had been pierced with 5-millimeter holes. As Live Science reports, the archaeologists believe the feature was meant to create an intimidating whistling effect as the projectile plummeted towards Roman enemies.

The Burnswark Hill dig, being led by John Reid of the Trimontium Trust, is the first major archaeological project at the site in 50 years. Roman troops staged an attack on indigenous defenders in a hilltop fort there about 1800 years ago. The whistling cast lead bullets, which soldiers would have hurled at their foes with a sling, accounted for about 20 percent of the bullets uncovered there so far.

The fact that Romans had taken the time to drill holes in the weapons initially had the experts confused. Such a procedure would have taken a considerable amount of effort only to end up with projectiles that are less heavy and therefore, less damaging. Reid never considered that the holes were meant to make noise until his brother—inspired by his fishing lures, which have a hole in the side and make a whistling noise when he casts a line—suggested the possibility.

After testing replicas of the bullets, the theory was found to hold some water. The holes did indeed make mechanical whistle noises that Reid, writing in the magazine Current Archaeologydescribed as "eerily reminiscent of an agitated wasp."

Whether or not the sound was used for intimidation is still up for debate, but the Romans wouldn't have been alone in using similar objects to antagonize their targets. In ancient China, Shàojiàn or "shrieking arrows" were used to startle animals between release and impact. And this video shows an example of the "death whistles" that may have been played by Aztec soldiers when marching into battle to psych out the enemy. (Take a listen: The unsettling sound lives up to the instrument's morbid name.) The Burnswark Hill bullets mark the first of their kind ever uncovered from an ancient Roman site.

[h/t Live Science]

All images: John Reid/Trimontium Trust via Twitter