Bridges Curriculum Extension Unit The engineering and construction of bridges has been in a constant state of change since early man first rolled a log across a stream to cross over to the other side. The earliest bridges used a beam of wood to span short distances. The Romans first created the graceful arch bridge and then a stronger material called concrete for bridges and buildings. In the 19th century, the triangular truss design stiffened bridge frames so they could span greater distances. As the Industrial Age introduced the need for stronger and longer bridges to carry trains and automobiles, steel suspension bridges added a new shape to the horizon. During this unit, student engineers experiment with balancing opposing forces using various bridge designs and materials.