Final answer:
The Incas needed suspension bridges for their road systems to overcome the difficult and varied landscape of their empire and to ensure safe passage for their armies and goods.
Step-by-step explanation:
The Incas needed suspension bridges for their road systems because the Inca Empire included large mountain ranges, canyons, deserts, and narrow coastal valleys. Travel and communication were difficult in this extreme landscape, so they needed technologically sophisticated road and bridge systems to connect their vast domains. These suspension bridges made of rope, stone, and wood were used to span numerous canyons and provide a safe passage for the Inca armies and the transportation of goods between provinces.