In old Venice citizens for centuries were used to wear masks in everyday life, not only during carnival times. The reason was simple: This vibrant, international and multicultural business town was crowded and comparatively small. As an island, it was not so easy to leave it. To get somewhere, you had to walk narrow streets or use small boats floating through narrow channels. Most citizens knew each other, so it was nearly impossible for them to go to a business meeting, to a friend, to your love or to the casino without being seen.
To solve the problem, the use of masks came up. It was acknowledged and regulated by the government. The mask itself was standardized to be suitable for official political events when all citizens were required to act anonymously as peers. Only citizens had the right to use it.
It was not allowed to wear weapons along with the mask, and police had the right to enforce this ruling. So whenever you met someone wearing the mask, you could be reasonably sure that he or she was a legitimate citizen of Venice with some accountability and that he or she was unarmed.
The mask I am talking about is the Bauta. If you ever had a look at old Venetian paintings, you will probably have seen this small white mask leaving the mouth part of the face open for talking, eating and drinking. It was usually accompanied by a black cape and a tricorn.