In a prearranged drill this afternoon, Capitol Police evacuated tourists and employees at the Library of Congress’ Jefferson Building, blocking off First Street between Independence Avenue and the Library.

Sirens in the Jefferson Building were sounded and hundreds of library employees were evacuated in the drill that involved dozens of Capitol Police officers.

Library employees were allowed back into the building about an hour later, shortly after 3 p.m.

A Capitol Police spokeswoman, Sgt. Contricia Sellers, said the drills take place on an ongoing rotation.

— Emily Yehle