Try folding it twice lengthwise and rolling it into a tube. This newspaper tube is strong enough to hold up a book. Beam bridges can span a greater distance with a thicker beam. But there is a limit, because too thick a beam will sag into the river. A truss is extremely strong and stable.
Shape is important for strength, but so is the material.
Wooden bridges will not hold as much weight as steel. Today, bridges are built of steel and reinforced concrete. Reinforced concrete beams are created by placing steel bars into the concrete before it hardens. This skeleton of steel helps the concrete withstand the tension that develops when long, unsupported beams are subjected to bending under heavy weight loads. The CN Tower, in Toronto, at 553 metres, is still the tallest free-standing structure in the world.