A long time ago I ran across this 1991 book at my parents' house, and read it over my weekend stay. It was well-written and wry enough that I re-read it a couple more times on subsequent stays.
It's about a guy, and his friend, who decide for no particular reason to build a big trebuchet, using original materials and design. The book is full of research and history and dark humor about the development of warfare. It's as much a meditation on human nature as a construction story.
Remembering it the other day, I had to order a copy. Dunno what happened to my parents' copy.