“You guys, just say ‘skooozy’ and walk through,” a young American woman commanded her friends, caught in one of the bottlenecks of tourist traffic that clog Venice’s narrow streets, choke its glorious squares and push the locals of this enchanting floating city out and onto drab, dry land. “We don’t have time!”

Neither, the Italian government worries, does Venice. Don’t look now, but Venice, once a great maritime and mercantile power, risks being conquered by day-trippers.