Rialto Bridge, Venice

The Rialto was Venice's commercial heart—its markets, banks, and warehouses—centuries before the bridge existed. Wooden crossings repeatedly collapsed or burned, so in 1588 the city held a competition for a stone bridge; entries reportedly came from Michelangelo, Palladio, and Sansovino, but the commission went to the aptly named Antonio da Ponte. Completed in 1591, his daring single 28-metre arch springs across the Grand Canal on some 12,000 timber piles driven into the mud, carrying two rows of shops up a central ramp. Sceptics predicted collapse; it has stood for over four centuries. For nearly 300 years it was the only bridge spanning the canal, the throbbing junction of Venetian trade.