The serjeant at arms was a personal attendant upon the King, especially charged with arresting those suspected of treason. Richard I had 24 with him on the Crusades. They were formed into a 20-strong Corps of Serjeants at Arms by King Edward I in 1278, as a mounted close escort. In 1399 King Richard II limited the corps to 30 Serjeants, and King Charles II had 16. The number was reduced to 8 in 1685 and since then it has gradually declined.
The original responsibilities of the Serjeant at Arms included "collecting loans and, impressing men and ships, serving on local administration and in all sorts of ways interfering with local administration and justice." Circa 1415, the British House of Commons received its first Serjeant at Arms. From that time onwards the Serjeant has been a royal appointment, the Serjeant being one of the Sovereign's Serjeants at Arms. The House of Lords has a similar officer.
The formal role of a Sergeant at Arms in modern legislative bodies is to keep order during meetings, and, if necessary, forcibly remove any members who are overly rowdy or disruptive. A Serjeant at Arms may thus be a retired soldier, police officer, or other official with experience in security. In recent times, however, the positions have often become quite ceremonial in some countries, with actual ability to eject members not necessarily being a primary requirement. The Serjeant at Arms of the House of Commons has general charge of certain administrative and custodial functions, as well as security within the chamber of the House.
The Knesset of Israel has a sergeant-at-arms (officially known in Hebrew as "קצין הכנסת" ("katzin ha-Knesset"), lit. "Officer of the Knesset", but as "sergeant at arms" in English). The sergeant-at-arms is the commander of the Knesset Guard.
The two houses of the United States Congress have also adopted the Sergeant-at-Arms. (Main articles: United States House Sergeant at Arms & United States Senate Sergeant at Arms) In both cases, the sergeants are charged with the maintenance of order on the floor of the chamber (in the House, he may "display" the mace in front of an unruly member as an admonition to behave); they serve with the architect of the Capitol building on the commission that oversees the Capitol Police and security for the Congress, and they serve a variety of other functional and ceremonial roles.
In imitation, a variety of other bodies -- from state and local legislative houses (city councils, county legislatures and the like) to civic and social organizations -- have created posts of sergeants at arms, primarily to enforce order at the direction of the chair and to assist in practical details of organizing meetings.