 It is the fourth of de Camp's historical novels in order of writing, and second chronologically, set in the time of Dionysios I of Syracuse at the end of the 5th and beginning of the 4th centuries BC.The protagonist is the engineer Zopyros of Tarentum, a follower of the Pythagorean philosophical school.Having invented an improved type of catapult, he is drafted into Syracuse's war effort against Carthage by the tyrant Dionysios, creator of the first military ordnance department known to history.