Washington DC is a highly political city but it will not have seen many days like this one.
They came from across America, hundreds of thousands of students, their families and their supporters, filling the streets around the White House and Capitol Hill.
In number and in voice it was the loudest and most impressive event of a campaign which shows no sign of going away.
It was a day of celebration of what they have achieved so far, a day of hope for what is to come and also, of course, a day of commemoration for those who have lost their lives to gun violence.
It drew celebrity support aplenty. From the Clooneys, Miley Cyrus and Jennifer Hudson, but the most powerful voices belonged to the student survivors of the Parkland shooting in Florida.
Through their tears they called for action, for politicians, who have so far been deaf to pleas for change, to finally sit up and listen, and for the President to side with them rather than this country's all powerful gun lobby.
The students want comprehensive gun control legislation right now.
But they are not going to get it and that is the real issue here.
They can organise as many marches and concerts and vigils as they like but none of it will alter the cold facts of this debate.
There remains in America a very powerful gun lobby that is resistant to persuasion and certainly resistant to change.
An NRA (National Rifle Association) member I spoke to at a gun show in St Louis told me there was no way they would allow national policy to be formulated by a "bunch of immature students".
The latest polling shows that 69% of Americans think gun laws should be tightened.
But it is the politicians – many of them Republicans, in the pay of the NRA – who will decide this issue.
And there is little indication that they will sign up for the kind of change being demanded by these students.
In truth, changing gun laws means changing a culture and that really is not easy to do.
But the momentum is with this campaign and the real test will be to develop a movement driven largely by emotion into a political force to be reckoned with.
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It could well happen, if young voters side with politicians backing gun control in the mid term elections; and if many of the leaders of the March For Our Lives even campaign for political office themselves someday.
But it requires change to Congress before there will be change to gun laws.