April 15, 2013, saw terror visit one of the world's oldest and greatest sporting events: the 117-year-old Boston Marathon.
Two bombs. Three killed. 183 injured.
It was an unspeakable tragedy for the victims, their friends and families; for the organisers; for the people of Boston and the United States; for all right-thinking people of the world; and, sadly, for the sport of marathon running.
Late last year I was training for and had planned to run in the 2013 Boston Marathon with a friend who had run it in 2008 for a young woman affected by neurofibromatosis.
My nine-year-old daughter was going to wait for us at the end of the 42km route with members of our respective families, cheering us on, quite conceivably in the spectators' area where eight-year-old Martin Richard of Dorchester, Massachusetts, lost his life and his sister and mother were gruesomely maimed.
In 2008, my friend had hugged her friends and family in the very same spot after the race.
In 2013, two relatives of the young woman my friend had run for in 2008 had their legs blown off. A young man known to her from Danvers, outside Boston, rushed to the aid of young Martin and, from what I've been told, is now struggling with what he saw and trying to grapple with why that little boy's life was taken and not his.
Circumstances changed for me and I didn't go to Boston.
I stayed home with my daughter and heard the news about what happened on Boylston St like everyone else.
The little boy who was killed could easily have been my little girl.
It is a thought that haunts me, just as the image of young Martin with his cardboard sign saying, "No more hurting people - Peace" haunts me and so many of us as we struggle to understand how and why this could have happened.
Especially so at an event that does so much good for charity and to a sport that nobly encourages every one of us, no matter our background, no matter our circumstances in life, to realise our potential.
In 2013, the last mile of the 26-mile race was dedicated to the families of the victims of the 2012 Newtown massacre.
When the bombs went off, those families were in the grandstands on the other side of the street.
After this week many amateur runners around the world will be thinking twice about entering their local half- or full marathon for fear that they too may be affected by the senselessness and gutlessness of terrorism. Marathons - open-air events free to public spectators - are an easy target.
But one cannot live in fear. That is not a life lived. They must go on doing what they always have. Just as the people of Boston - the most generous, unpretentious, proudest and strong-willed collection of men and women I've ever had the pleasure of coming across in years of travelling to the United States - have gone on with their lives.
The way they came without fear, lined up and stood as one to sing the national anthem before the Bruins game at TD Garden on Wednesday was unforgettable. They showed that the best response to such a tragedy is to carry on.
Let's keep on running.