Authorities evacuated portions of Harvard University on Monday after they received an emailed bomb threat.

After two hours, officials called Emerson and Sever Halls safe while still investigating the Science Center and Thayer Hall.

Emails and texts alerted students at 12:30PM ET about the bomb threat. The police cleared out Harvard Yard and locked gates around campus.

Executive Vice President Katie N. Lapp sent out an email at 1:40PM telling the university that “nothing to substantiate the emailed threat has been found.”

Authorities reopened the Johnston and Widener Gates but asked students about their activities before they allowed them to enter Harvard Yard.