It's an unprecedented response to the awful events which took place in Paris this week with the attack on Charlie Hebdo.
The aim of the terrorists is to create fear and division between muslims and non muslims, not just in France but across the West. Today's march and the reaction around the world has shown that this aim has failed and will continue to fail.
On an average day I rarely think about the ideals and values of the society that I live in. The attack on Charlie Hebdo has changed that. The week's act of terrorism is an attack on all of us.
It goes beyond the murder of innocent individuals, it's an attack on the values and beliefs that many of us in the West hold most dear. This is why there has been such a response.
Like many people outside of France I had never heard of the magazine Charlie Hebdo but I understand the value and importance of freedom of speech, expression, the role that satire plays in a free society. I find it offensive that the terrorists think they can stop this!
I'm beginning to take the view that Islamic extremism has very little to do with religion. It's simply nothing more than criminality hiding behind religion mixed in with the ideas of a death cult.
All religions are essentially belief systems and as such should be open to scrutiny, they should be challenged, questioned and when appropriate they should be mocked. Islam cannot be an exception to the rule.
Once today's rally is over, there are of course many further questions that need to be asked. Most importantly why people who have grown up in Britain and France and other Western countries feel the need and desire the reject the values of the societies they have grown up in and travel to the Middle East to take up radical extremism.