For an idea of the kind of power wound up in these engines…

"And any one may learn the force of the engines by what happened this very night; for as one of those that stood round about Josephus was near the wall, his head was carried away by such a stone, and his skull was flung as far as three furlongs (600 meters). In the day time also, a woman with child had her belly so violently struck, as she was just come out of her house, that the infant was carried to the distance of half a furlong (100 meters), so great was the force of that engine. " - Flavius Josephus

“In the course of these contests a builder on our side, whose name I do not recall, happened to be standing behind a scorpion, when a stone which one of the gunners had fitted insecurely to the sling was hurled backward. The unfortunate man was thrown on his back with his breast crushed, and killed; and his limbs were so torn asunder that not even parts of his whole body could be identified.” - Ammianus Marcellinus