Members of Congress, their staffs, their families, and visitors to the Capitol are protected by the United States Capitol Police.
The Capitol Police were official founded in 1828 with three non-uniformed watchmen. Before that, only one guard protected the Capitol. Today, more than 1300 professionally-trained men and women serve as Capitol Police Officers.
The Capitol Police in 1900.
Members of the Capitol Police in 1973.
Images courtesy Senate Historical Office http://www.senate.gov/learning/learn_history.html These images may be restricted by copyright. Please contact the Photo Historian at 202-224-6900 for copyright and ordering information.
This information is paraphrased from the book "The Young Oxford Companion to the Congress of the United States." Used with kind permission of the author, Donald A. Ritchie