The instructions below are for a pentagram-shaped fort. You can also use your imagination to design your own fort!  Try building flat walls, or putting four triangles together to form a pyramid with triangle sides (a shape called a tetrahedron).

1. Make newspaper rolls from two sheets of flat newspaper. Use open, two-page spreads, not single sheets. Roll them tightly from corner to corner -- the tighter the roll, the stronger the support. Secure with tape. You'll need 37 rolls.
2. Use three newspaper rolls to make a triangle, attaching at each corner with staples. Make 11 triangles. The last four newspaper rolls will be used for bracing your fort.
3. Prepare the base of your fort. Lay five triangles flat on the ground so that the triangle bases form a line with the tops all pointing up. Attach the triangles to each other along the bottom edge with staples and / or tape. 
4. Prepare the middle layer of the fort by attaching four triangles to each other in the same way.
5. Make a pyramid for the top by attaching the last two triangles at their tops, opposite each other, and using two straight newspaper rolls to complete the square base.
6. Get someone to help hold your fort as you put it together! Take the bottom layer of five connected triangles and shape it into a pentagram, attaching the two bottom corners together. The triangle points should point upward somewhat but will tend to fall over, and that's OK.
7. Take the middle layer of four triangles and and position them on top of the bottom layer so that the bottom corners touch the pointed tops of the layer below. Twist pipe cleaners around each spot where the two layers join. As you work your way around, the fort should be more upright!
8. Place the pyramid on top and attach at the corners with pipe cleaners.
9. Use the last two newspaper rolls as braces to form a diamond-shaped doorway, securing with tape. The fort should be sturdy but feel free to add tape or even craft sticks to reinforce any wobbly areas.

The fort's shape can be hard to visualize! Check out this document for some additional visual instructions. 

What's happening?

Triangles are considered the strongest shape because they can handle heavy loads without collapsing. Hold one of your newspaper triangles and apply some force on the sides; the triangle should feel sturdy and hold its shape. If you put force on a square or rectangle, the shape can tilt or collapse. The triangle’s strength is why architects use it often in structures.

Bridges are made up of trusses, which are triangles that share sides and connections. Look for triangles the next time you see a bridge or a building being built. You can also find them in a geodesic dome, which is a spherical or partially spherical structure formed from triangles. You can find geodesic domes on playgrounds as climbing structures. Another example is the giant sphere at Epcot.

Recommended reading

The Savage Fortress by Sarwat Chadda

The Three Little Pigs and the Somewhat Bad Wolf by Mark Teague