The siege engine's crew loaded the counterweight and took aim at the castle wall.
The weight was dropped, the lever triggered, the long arm whipped overhead — to sling a tennis ball toward the formation of cardboard boxes on the other side of the room.
During the late Middle Ages, instructor Eric Slyter said, the trebuchet was one of the most feared siege machines of its day. Much larger than the 5-foot-tall model that Slyter brought to the Tigard Public Library on Friday, July 14, the weapon could propel heavy rocks, flaming tar and other projectiles across wide distances with enough force to break through castle walls.
Slyter is director of the Knights of Veritas, a group based in Ellensburg, Wash., with a goal of accurately teaching medieval history and displaying true-to-life artifacts and replicas from the era.
On Friday, Slyter invited Tigard Library patrons from ages 10 to 18 to try both loading and firing the trebuchet to knock down the cardboard "wall," and designing and assembling the cardboard boxes to form a more impregnable defense.
In addition to teaching students about medieval warfare — always an attractive hook — the exercise provides lessons on engineering and physics.
"We trick them into learning while letting them play with a model war machine," Slyter said.
Another objective of the Knights of Veritas in providing such lessons is to give kids and teenagers an appreciation of the science and technology of the Middle Ages.
"When we can kind of break down how they did things in the Middle Ages, we're more prone to give them credit for what they accomplished," Slyter said. "It's very easy for 21st-century people to say, 'Ugh, people back then were savages, they didn't know anything.' But when you actually look at the buildings that they made in the Middle Ages and the machines that they designed to knock those buildings down, and the combat art and the sciences that they were applying, not only was their science very good, but they were trying, they were experimenting with it."
He added, "I think it helps people develop an appreciation for people of the past that they might not otherwise have."
That wasn't lost on Eli Webster, an incoming freshman at Tigard High School.
"It was genius for the time," Webster said of the trebuchet.
Webster and Kyler Bonwell, who will be a freshman at Lakeridge High School, said they came to the library program because they like the subjects of medieval history and warfare.
"Siege equipment's my favorite," said Bonwell.
While Bonwell, Webster and Cody Bonn engineered their cardboard castle wall to be extra-thick and low-profile, once the trebuchet crew figured out how heavy to make their counterweight and how to set the siege engine's sling so it would throw the tennis ball accurately, they found themselves cringing as their carefully arranged boxes were scattered by a direct hit.
Their experience was just a taste of what the inhabitants of fortresses in the Middle Ages would have felt when menaced by the trebuchet. Slyter told students that the weapon was so intimidating that sieges were often settled by parlay, as a castle's occupants would fear it being used against their works. There are even recorded instances of trebuchets being used to fling human and animal corpses into enemy positions to spread disease, an early use of biological warfare.
Friday's trebuchet demonstration was part of the Tigard Library's "Build a Better World" series of summer programming for teens.
"Today, we're not only going to be building a better world, we're going to be knocking a better world down with our trebuchet model," Slyter quipped.
The Knights of Veritas have been conducting summer programs at the library for more than a decade, Slyter said. They also have a swordfighting presentation, which was not part of Friday's library program, that contrasts "theatrical" sword combat, of the sort seen in movies and television shows, with the historically accurate way medieval swordsmen actually fought.