They kept running. That was their instinct. They had made it almost the whole 26 miles and 385 yards, through Ashland and Framingham and Natick, past Wellesley and Boston College, up and down Heartbreak Hill. Now they were on Boylston Street, in Copley Square, and they could see the finish line when the world exploded.

I keep watching them run. The guy in the pink shirt. The woman in the lime-green top. They might've been delirious. A marathon can do strange things to your mind. But somewhere in there is that desire, strong as a runner's calf, to finish what you set out to do.

They started running. That was their instinct. Seconds after the blast, police officers and rescue workers and soldiers in fatigues ran toward the danger instead of away from it. They took down the barricades that blocked off the street and they helped the wounded. That comes from years of training, of course, but it starts from the desire, strong as a runner's quad, to help other humans who need it.

Running is the simplest sport. Little kids run because they can. As we grow, we run to test ourselves. A marathon, for most people, is not about speed. It's about survival. It's about embracing pain and finding the will to defeat it.

We don't know, as I write this on Monday evening, exactly what happened in Boston. It looks like bombs. At least three people are dead and more than 100 are injured. I saw a photo of a man being wheeled down the street. He was missing the bottom half of his leg. I never want to see that photo again.

Now that I'm a sportswriter I spend a lot of time in football stadiums and ballparks and arenas, and every time I think, what an easy target for an evil mind. A Super Bowl would have too much security. But a regular-season football game would have just as big a crowd. More than 23,000 runners entered the Boston Marathon. Add in hundreds of thousands of spectators all along the route. Those officers at the finish line were there to keep the runners separated from the crowd. I doubt many were there watching for bombs.

They will be now.

I've been there on Boylston right where the bombs went off. It's just down from Copley Square, one of the most beautiful parts of a great city. Trinity Church, with its priceless stained glass, stands across the street from the Boston Public Library. On Marathon Monday -- Patriots' Day -- the Red Sox play in the morning, and fans walk over after the game to watch the runners finish up. It's the unofficial first day of spring.

On Monday, the Red Sox won. By the time the race clock hit   4:09:43, the marathon winners were already relaxing. The ones still on the course were the grinders. It was a day of joy and achievement.

If we could only freeze it there, before 4:09:44, before the flash and the smoke and the shock wave that rippled the banners. But we don't get to do that.

They kept running. That was their instinct. As everybody started sorting out what happened in the chaos right after, it turned out that some of the marathoners did a remarkable thing. They crossed the finish line and kept running, right to nearby hospitals, to give blood to those who were injured.

This is the race life has given us. The clock keeps going, and we have to keep running. We don't even know where the finish line is. We just have to gut it out.

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Questions? Comments? Challenges? Taunts? You can reach me at tommy.tomlinson@sportsonearth.com or on Twitter @tommytomlinson.