There were nearly 600 children on the island that day. The attack with high-powered rifles by Anders Behring Breivik lasted 72 minutes.
He killed 69 of them, half of whom were under 18, and wounded 66. That's a person shot every half minute. He was a very busy boy, hoping all the time, he says, that the police would arrive and take him down.
This was evil on a grand scale. Those numbers are staggering. Mind you, I suppose they don't really compare to the mass killings by the Nazis and by Stalin.
In a magnificent television series called Russia's War: Blood Upon the Snow, an exhaustive and exhausting series about the Great Patriotic War with extraordinary footage from the Russian archives, the Russians, after the war, discovered one mass grave containing in excess of 120,000 bodies.
Most were shot on the edge of a massive pit and simply fell in. It is hard to conceive of a world where this happens but while we must never forget the human capacity for kindness and good, neither should we ever forget the human capacity for evil. There are plenty of recent examples of evil on massive scale, Pol Pot in Cambodia, the killings in Rwanda, and the work of Ratko Mladic in Bosnia just a few years ago.
And that evil can come along out of the blue, as Breivik showed. An innocent sunny day and a madman is walking among kids at an idyllic summer camp firing the meanest-looking guns left right and centre, in order, he says, to cleanse Europe of filth.
And I got to thinking about Breivik and grief and human strength because this week, several hundred of the surviving young people went back to the island.
And some strolled along the shore where they may have run or hidden or played dead or dived into the water and swam like hell. And I wondered how anyone could ever recover from having gone through the infamous 72 minutes, having seen the carnage, the mass murder all around.
And I wondered if having seen the carnage makes it easier to grieve, because you lived through what happened, you saw it. Or whether, having seen it, you've added a gruesome picture in your mind, which will play in your brain forever, year in year out.
Either way, grief is always immense, I know, when a loved one is taken suddenly but horror is horror nevertheless. Having seen horror must add an awful extra layer with which a grieving person has to cope.
Talking of grief and terror and horror, I've been reading the memoirs of some of the RAF Bomber Command crews.
I don't know how those air crews coped with it all, flying nightly as they did on long, cold missions into vast walls of anti-aircraft fire. And when they bailed out over Germany, naturally enough, I suppose, they were often badly beaten by local people and police and the SS. I guess matters like survival and getting home were a lottery. If your name was on it, you copped it and that was that. The tail gunners felt the terror first. You were helpless and isolated in the tail. The fighters came from behind and got you first. Aircrew reckoned you had 11 hours' average flying time in the tail over enemy territory before you were killed.
And the RAF didn't always handle the grief of the aircrews nicely either. The worst disgrace, a fellow who was broken had to endure having LMF stamped on his papers as they let him go and work in the kitchens. LMF: Lack of Moral Fibre. Hardly.