This study investigated why the design of ancient throwing machines evolved from eutitonon (arms outside the mainframe) to palintonon (arms inside the mainframe) from the end of the first century B.C. to the first century A.D. and evaluated the mechanical advantages of the new design. Palintonon was first used for big machines; in the following centuries, it was also used for much smaller machines. Essentially, the palintonon design has several advantages: more elastic energy can be stored in the hair bundles representing the motors of these machines, heavier projectiles can be thrown with the same charging effort, projectiles are stressed by lower acceleration in the machine with the same muzzle velocity, and the throwing machines have higher efficiency. Results are also presented regarding the “internal ballistics” of these ancient throwing machines by using simulation software.