architect Paolo Soleri believed that humans were migratory creatures and wanted to design high density cities (to minimize their impact on the environment) where they could stop between their travels. He built Arcosanti in the Sonoran Desert to test his ideas. His 'Beast' bridge (shown above) was designed to help carry his imagined tribal societies on their journey. It's a continuous concrete structure with the superstructure folded upward at midspan and folded downward at the supports. It actually looks a lot like Frank Lloyd Wright's 'Butterfly' bridge, which isn't surprising since they worked together at Taliesen in the 1940s. Most likely, they influenced each others designs. This bridge was in 'The Architecture of Bridges," a book that The Happy Pontist rated highly in a blog last week.