Roman Arch Bricks
Here's a teaching tool that shows students how blocks were shaped to make Roman arches. The bricks are made from 3mm cardboard. It is sized to make the largest possible brick on a 18" x 24" laser bed. If you print nine of these, you can make a roman arch.
Tape is not needed to hold these together (it was used by students in their "dig" to show they'd tampered with the site). Students were first paired in teams of two and told to build the arch together. Once they figured out how to do so, they could work with other teams and build objects that used multiple arches. In the pictures you can see them trying to build an aqueduct, dome, etc.