We had to try this out to see how well it worked, and we're pleased to report it works really well! You can build a bridge with toothpicks and mini-marshmallows, and it's easier than using glue, although the bridges you build won't support quite as much weight. The basic building blocks of your bridge will be tetrahedrons, as shown on the right. The structures you make will be made from many of these, joined together. Here is a beam made by joining several tetrahedrons together. Notice that adjoining tetrahedrons share marshmallows; this isn't strictly necessary, as pieces can be attached together by running pieces of toothpicks between adjacent marshmallows. We'll do that when we want to join several structures ... see below. Quite complicated arrangements can be put together. Here we've joined several smaller structures with short lengths of toothpicks, rather than sharing marshmallows between adjacent pieces. This makes construction easier, as you can make several identical modules first, and then easily join them. Your fingers do tend to get a little sticky, though! Here we balanced a book on four of the individual tetrahedron pieces, to show you how strong the construction is. However, we discovered that fresh marshmallows tend to let the toothpicks slide too much, so the strength of an actual structure shouldn't be tested using weight until the marshmallow bridge has been allowed to sit for a few days, to let the marshmallows get hard. Plasticene might be a better choice for serious bridge builders! Grade 7 and 8 classes tried building towers and bridges using marshmallows, plasticene, spaghetti, and plastic straws. I took pictures of their efforts, which you can see here. Introduction Bridge Structures | Bridge Photos | Using Toothpicks | Marshmallows | Make a Plan