A bridge in Pittsburgh, Pennsylvania, USA. Pittsburgh has more bridges than any other city in the United States. The city's history as a steel producer, railroad and shipping center, as well as it and it's proximity to three major rivers and countless hills and ravines, has led to its becoming known as the City of Bridges. (Australfoto/Douglas Engle)

A bridge in Pittsburgh, Pennsylvania, USA. Pittsburgh has more bridges than any other city in the United States. The city's history as a steel producer, railroad and shipping center, as well as it and it's proximity to three major rivers and countless hills and ravines, has led to its becoming known as the City of Bridges. (Australfoto/Douglas Engle)