Originally, the masks were worn daily; and by doing so the wearer could hide his or her identity and status. A high born lady could wander the streets of the market, a common man could pass himself off as a successful merchant. The masks also allowed the wearer to act more freely without the constraints of their given social class and ignore the boundaries that would otherwise apply. This was especially true at a party, where the host would not have known whether the wearer was high born or not but could not risk offending invited guests, and so would have to have welcomed everyone wearing a mask. This is what makes the story of the Montagues sneaking into the Capulet masked ball without detection plausible (Romeo and Juliet).
However, given the possibility, the mask could be used for good as well as bad intent; one might sneak out from their manor house to speak with their lover in another part of town, opinions might be more openly voiced in conversation, or a knife might find its way into an enemy's back. Who was that masked man? Nobody knows.
Therefore, the daily use of masks was restricted - almost disappeared except for on rare occasion. Then, in 1162, a festival was held to commemorate a military victory. The festival became an annual tradition, and as it developed and became larger and more colourful each year, the Carnevale di Venezia was born. The masks became more and more elaborate and the balls, dances and parties lasted for days. That is, until 1797 when the King of Austria outlawed the Carnival and strictly forbid the wearing of masks.
Over the next 200 years, masks were usually only worn at private parties or at exhibitions as part of an artistic expression. In 1980, a Carnival revival began in an effort to attract tourists to Venice.
There are three popular types of masks worn at Carnival. The first is the Bauta, which hides the whole face, but extends away from the lower part of the face so that the wearer can still eat. The extension also acts as a tunnel and alters the voice of the wearer, furthering the disguise. A Columbina is a half mask, which is often highly decorated with feathers and silk flowers, and is either held up to the face by a baton or tied around the head with a ribbon. Medico della Peste (the Plague Doctor) is the third type of mask, which got its ominous name from the Plague in Italy during the 17th century when it was worn as a precautionary measure against contracting the disease. It is easily recognized with its long beak and stark appearance without decoration.
Today, you can find masks pretty much everywhere you turn in Venice. Some are authentic and made in Venice. Most are not.
Tonight is the staff party for work, and the theme is Masquerade, which is a type of masked ball. Perhaps we will see if people do indeed act more freely behind the guise of a mask (there is no worry that some one with ill intent pulls a dagger out before running off into the darkness of the night). I'm sure it will be a lot of fun.