STEM teachers looking for a hands-on unit to pique their students' interest in engineering may want to check out this activity available through TeachEngineering. This activity introduces students to the trebuchet, a compound machine developed in the Middle Ages as a siege engine that can be seen today in events like Punkin' Chunkin'. Created with students in grades seven to nine in mind, the Trebuchet Design & Build Challenge takes place over ten 60-minute class periods. During this challenge, students work as teams to "design and build their own trebuchets from scratch while following a select number of constraints." They later test their designs, collect data, use quantitative analysis to evaluate their trebuchet's performance, and then give presentations on their design process and results. The Trebuchet Design & Build Challenge was developed as part of the Research Experiences for Teachers Program in the NASCENT (Nanomanufacturing Systems for Mobile Computing and Mobile Energy Technologies) Engineering Research Center at the University of Texas at Austin. TeachEngineering is a digital library of standards-aligned K-12 STEM teaching resources whose development was funded by the National Science Foundation and is currently managed by the University of Colorado-Boulder and Oregon State University.