Malamocco (or Metamauco) was capital of the Venetian proto-state for parts of the 700s, possibly located on the Lido di Venezia.
The Birthday of Venice of is traditionally on March 25th, 421 CE, but this is far more legend than historical truth.
Venice was a republic from the beginning, but in a time when hereditary power was the norm, why did Venice become a republic and not a monarchy?