Why engineering mattered
Railroads need relatively gentle grades and broad curves compared with ordinary roads, so mountains, rivers, and valleys created enormous engineering challenges.
Bridges
Timber trestles, masonry arches, iron bridges, and later steel structures allowed railroads to cross rivers and deep valleys while carrying increasingly heavy trains.
Tunnels
Tunnels shortened routes through mountains but demanded dangerous excavation, ventilation, drainage, and substantial capital.
A permanent footprint
Many nineteenth- and early-twentieth-century railroad engineering works still shape transportation corridors today.