Capitol police in the United States are agencies charged with the provision of security police services for various state agencies, but especially state legislatures. Capitol police may function as part of the state police or may be an independent agency. There is also a federal capitol police agency.
Security police for government facilities are a very old idea, dating back at least to the guards posted at Solomon's temple and including such units as the Praetorian Guard and the Coldstream Guards.
The United States Capitol Police is the agency charged with the protection of the United States Capitol and some surrounding buildings, including the Library of Congress.[1]