Whether as a Casanova, courtesan or noblewoman, the Venetians celebrate ten days their carne vale (Latin for saying farewell to meat), for centuries in colorful costumes with mask.
The masks have a looong tradition here. With them they could (and still can) enjoy the illusion to be someone else. Indeed this symbolizes the Janus-facedness of the Serenissima: Showing by hiding.
Read more on the history of the Carneval of Venice.