There was a public response to the bombings in Brussels yesterday. A large mass of people gathered in Place de la Bourse to express their grief and, I hope, their resistance to Islamic extremists. Extremists that seek to destroy the society that has given them freedoms that they never could find in their home countries. But was this expression of grief and resistance enough? Brussels is the capital of Europe. On January 1, 2015 It had a population of 177,307. Of this population, how many people stood up to be counted at the event? We can see from a photograph by Martin Meissner/AP that a very dense crowd filled the square. But how large a crowd was it? By finding the Place de la Bourse with the CrowdSize application and performing a calculation consistent with what we see in the photograph, we find that approximately 11,800 people attended the event. This is 7 percent of the population of Brussels. More people need to stand up and be counted and action needs to be taken if the threat posed by Islamic terrorists is to be defeated. Flowers, candles and messages in chalk are thoughtful but are not enough. The enemies of our way of life can see this.