The counterweight trebuchet was the heavy artillery of the Middle Ages, using gravity to hurl projectiles and destroy fortifications. Some trebuchets may have been almost ninety feet tall, and several likely threw stones weighing more than three hundred pounds farther than four hundred yards. While replica historical machines have been made in modern times, the methods of building and assembling trebuchets have not been widely published. Learning how these machines were built can tell us about the logistical difficulties of sieges and the sophistication of medieval engineering and technology. Information gleaned from several extant technical drawings and manuscripts, and the traditional techniques seen in medieval buildings and ships, was used in conjunction with experimental history to reproduce a small machine at full scale (thirty-three feet tall). Here, I show how something so large can be assembled with traditional hoisting equipment that dates to ancient times. This project highlights the expert craftsmanship of the high-late medieval period and shows that engineers of the Middle Ages knew how to use simple machines to accomplish the complex task of assembling a large trebuchet.