The Rialto Bridge is the oldest of the four bridges spanning the Grand Canal in Venice, Italy. Connecting the sestieri (districts) of San Marco and San Polo, it has been rebuilt several times since its first construction as a pontoon bridge in the 12th century, and is now a significant tourist attraction in the city. The present stone bridge, a single span designed by Antonio da Ponte, was finally completed in 1591. It is similar to the wooden bridge it succeeded. Two inclined ramps lead up to a central portico. On either side of the portico, the covered ramps carry rows of shops. The engineering of the bridge was considered so audacious that architect Vincenzo Scamozzi predicted future ruin. The bridge has defied its critics to become one of the architectural icons of Venice.