The all-clear has been given after report of gunshots at one of the US's most prestigious universities.
Princeton University said earlier that police had cordoned off Nassau Hall after public safety officials received a report of gunshots.
Officials at the the Ivy League university in New Jersey later said the reports had been determined to be unfounded and reopened the area.
Princeton's website calls Nassau Hall the centrepiece of its campus and a university and national landmark.
It says classes moved from Newark to Nassau Hall when the building was completed in 1756.