The Eiffel Tower, France's top tourist draw, was briefly evacuated on Sunday and the area ringed by security forces.
Police said the action followed a threat delivered by telephone but did not elaborate.
The famous monument was evacuated shortly before 4:00 pm (1800 GMT) and reopened about an hour and a half later.
Evacuations have been staged regularly at the Paris landmark, usually after bomb threats. There have been two such incidents this year, on March 30 and August 9.
On June 18 the monument was closed for two hours after a man threatened to commit suicide.
The Eiffel Tower is the world's most visited monument, attracting up to 32,000 tourists daily.AFP