No city stirs the imagination more than Venice. From the richly ornamented palaces emerging from the waters of the Grand Canal to the dazzling sites of Piazza San Marco, visitors and residents alike sense they are entering, as fourteenth-century poet Petrarch remarked, "another world." During the Middle Ages and Renaissance, Venice was celebrated as a model republic in an age of monarchs. In the seventeenth and eighteenth centuries, it became famous for its freewheeling lifestyle characterized by courtesans, casinos, and Carnival. When the city fell on hard times following the collapse of the Republic in 1797, a darker vision of Venice as a place of decay, disease, and death took hold. Today tourists from around the globe flock to the world heritage site as rising sea levels threaten its very foundations.