The City is a ceremonial county which has a Commission of Lieutenancy headed by the Lord Mayor instead of a Lord-Lieutenant and has two Sheriffs instead of a High Sheriff (see list of Sheriffs of London), quasi-judicial offices appointed by the livery companies, an ancient political system based on the representation and protection of trades (guilds). Senior members of the livery companies are known as liverymen and form the Common Hall, which chooses the lord mayor, the sheriffs and certain other officers.