We are a species of bridge builders. Since time out of mind, humans have engineered structures to surmount obstacles. Although the concept itself is as simple as felling a tree across a creek, bridge design and construction entails serious ingenuity. Artists, architects and engineers pour vast resources into bridge construction and, in doing so, reshape the very environment in which we live. As a result, we inhabit a planet of bridges, some as ancient as Greece’s 3,000-year-old Arkadiko bridge or as unchanged as India’s 500-year-old Meghalaya living bridges, which are coaxed into existence from growing tree roots. Countless others have fallen into the ravines and rivers they span, as humans continue to tackle ever more ambitious bridges and construction.