The backdrop was ideal for President Obama's initial message of a world that had changed beyond recognition. These were the gates through which Hitler drove to glory in his conquest of Czechoslovakia, this the castle in which Communist presidents used to receive like-minded leaders of the unfree world.
He told the crowd, estimated by the White House to be 20,000 strong that when he was born it was inconceivable that an American President "like him" would be allowed to speak to a crowd in Prague. What was impressive about the speech on nuclear disarmament was not the depth of his thought but the way he pulled disparate strands together to weave a coherent picture.
The audience stopped flag waving and cheering as the president's tone grew more serious. He told them that if Iran gave up its nuclear programme there would be no need for a missile shield in the Czech republic : the plan to station a radar here is hugely controversial and is stuck in Parliament.