The Boston Marathon is the oldest and most celebrated of the mass marathons. Monday's Boston was to be my fourth. I was running as a fund-raiser, this time for the Michael Lisnow Respite Centre.
You need to be in Boston on Patriots' Day to appreciate the celebration. A city of less than 1 million comes to a stop; people line the 42.4 kilometres and stay all day, cheering on every runner.
Picture Melbourne on Cup day or grand final day without the booze. Boston is high on its marathon and the runners.
Someone came to the marathon today with a different purpose than to celebrate. Someone whose malignity exceeds his knowledge: his bombs exploded near the finish around the four-hour mark; in an elite marathon like this, the ''bulge'' - the greatest concentration of finishers - occurs 30 to 60 minutes earlier. The terrible toll might have been much heavier.
I plodded to the 35-kilometre mark when a spectator offered me a slice of orange, his face troubled. ''There have been explosions near the finish line. The marathon has been temporarily suspended.''
Naively I ran on.
Police and runners were mingling on the course. Some wept wrenchingly, their features distorted in grief, or shock. Many had relatives waiting at the line.
The crowds fell quiet. Overhead, helicopters clattered. Police vehicles were racing everywhere, ambulance sirens shrieked.
Police turned back those of us still running. I needed to contact family. Strangers handed me their phone. I asked a teenager for directions to a local landmark where my relatives would be; the teen insisted on escorting me there.
As I waited, strangers stopped to offer help. One bloke wanted to give me his jacket so I wouldn't get cold. Passers-by touched me. One stopped, gazed at me, shaking his head. ''I am sorry,'' he said.
Boston silenced, in shock, in grief. Its citizens reaching out to each other in spontaneous solidarity. More than that, people felt implicated in a wrong, embarrassed: their guests had been hurt, frightened. They turn their goodness upon me and I feel like crying.
A terrible beauty born.
Howard Goldenberg is an Australian GP and writer.
