Sotto il cielo di Praga.
Czechs and Slovaks are marking the 20th anniversary of the Velvet Revolution - which brought down the Communist government of the then-Czechoslovakia.(Prague marks Velvet Revolution)
"The march set history into motion," said Mr Havel to applause.
In a speech to the Czech senate earlier on Tuesday, Mr Havel paid tribute to the memory of those who had helped to bring down the Communist regime, including his late wife Olga.
"We often tend to forget our fellow colleagues, friends and the open-minded people in everyday life," he said, going on to name dozens who had died since the protests.