The variety Axisand Siegeimportance of siegeSiege engines to ancient warfare is outlined and presented. Ballistas are described, and their origins and development are discussed in detail. A simple approximate expression for ballistaBallista projectileProjectile (either arrowArrow or rounded stone)Launch speed launch speedSpeed is derived, and predictions made for the ranges of ballistas. The “scalingScaling rules” of ancient ballistaBallista engineers are presented and explained; scalingScaling behavior is discussed more generally. BallistaBallista efficiencyEfficiency is estimated. The growth of ballistas during the period of their domination of European siegeSiege warfare is noted. Large and smallBenchmark “benchmark” ballistas are analyzed and their performances presented. These predictions compare well with the claims made by ancient sources of ballistaBallista capabilities, and with the performances of modern reconstructions.