When the lagoon was frozen
Many years ago, in the time period between the wars and the early 50 happened that large parts of the lagoon, due to the shallow water, ice cold completely.
People could get to Venice from the mainland, walking on the ice. The goods were transported on carts pulled by horses or donkeys.
For many years this does not happen anymore, because of global warming pollution as well.
The coldest period of the year is in late January, a period in Italy known as the days of the blackbird. According to legend, the blackbirds were white, but one day because of the cold, a blackbird took refuge in a chimney to give birth to its young. For soot, the blackbirds were born blacks, and blacks still remained from that day. It 'a legend, but a couple of years is around home a completely white blackbird!