Slavery was not a large part of Venetian culture or Venetian history, but there were slaves in Venice.
The Sestiere San Polo is in central Venice, around the upper bend and central part of the Grand Canal.
Fires were a very real preoccupation of the Venetians, and there have been many fires in Venice over the centuries
Venice is divided into six sestiere whose origin is as old as the city of Venice itself. As far as we know, they have always been there.
The Birthday of Venice of is traditionally on March 25th, 421 CE, but this is far more legend than historical truth.