Short answers, pulled from the story.
The traditional founding of Venice took place at the stroke of noon on the 25th of March 421. This event marked the dedication of the first church, that of San Giacomo on the islet of Rialto.
The original population consisted of fishermen known as incolae lacunae or lagoon dwellers who lived in the marshy lagoons. Some late Roman sources reveal these early settlers were part of twelve founding families known as apostolic families who elected the first doge Paolo Lucio Anafesto in 697.
Venice's long decline started in the 15th century when it confronted the Ottoman Empire in the Siege of Thessalonica between 1422 and 1430. Vasco da Gama's voyage from 1497 to 1499 opened a sea route to India around the Cape of Good Hope destroying Venice's monopoly.
Venice is situated on a group of 118 small islands separated by canals and linked by 438 bridges within the shallow Venetian Lagoon. Building foundations were constructed by driving closely spaced piles consisting of alder tree trunks into mud and sand until reaching compressed clay layers.
Napoleon Bonaparte conquered Venice on the 12th of May 1797 during the War of the First Coalition. He removed the gates of the Ghetto ending restrictions on when and where Jews could live and travel in the city before Venice became Austrian territory on the 12th of October 1797.
In 2021 there were 254,850 people residing in the Comune of Venice with 50,434 living in the historic city of Venice Centro storico. The city hosts up to 60,000 tourists per day with annual estimates varying from 22 million to 30 million visitors causing overcrowding and environmental problems.