Catapult: Harry and I Build a Siege Weapon

It all started when Jim Paul found out he couldn't bring a grapefruit-sized piece of two-billion-year-old quartzite onto the plane because, the attendant said, it could be used as a weapon. That's ridiculous, he thought, holding the rock in his hand. And then he realized that, at one time, such a rock had been a weapon, and a catapult had launched it. So was born the idea to build a medieval catapult, exact in every detail. And so was launched the book that has now become a much beloved classic.