European leaders have been told they must remain united, in the face of challenges facing the EU.
The call came from President of the European Council Donald Tusk at a ceremony to mark the 60th anniversary of the Treaty of Rome.
The Taoiseach Enda Kenny was among 27 leaders who attended - however British Prime Minister Theresa May wasn't there.
She's due to start the Brexit process on Wednesday.
Donald Tusk says European unity is not just an optional extra: