The Romans built bridges the way they built everything: systematically, durably, and in sufficient quantity that their combined effect transformed the physical landscape of three continents. More than 900 Roman bridges have been identified by archaeologists, ranging from small rural crossings to major river spans, and approximately 700 of these survive in some form. The number is less remarkable than the durability: bridges that have been carrying traffic — first Roman, then medieval, then modern — for two thousand years represent an engineering achievement that no subsequent civilization has equaled in pure longevity. Several Roman bridges in active use today are the oldest functioning bridges in the world.