This is part of the series of 30 exercises developed during the 3D4KIDS program. One of the aims of this Erasmus+ program is to improve the knowledge of teachers regarding the 3d printing technology by developing some specific training materials. More info in the website: https://www.3d4kids.eu/ This unit is about Structures and Technical Drawing. Students will work in a collaborative way by means of the project-based learning methodology. They will have to design, draw and build a semicircular bridge, using plaster for the wedge-shaped stones, throughout a 3D printed mould in the required size and evaluating its functionality by applying compression stress.