Last year, I sent an e-mail to Marie Colvin, the London Sunday Times journalist who was killed by government forces in the Syrian town of Homs earlier today. I was hoping to hook up with her somewhere in North Africa, where we were both covering the Arab Spring.

I asked her to be careful because things looked complicated and scary in Libya. On February 22—a year ago today—she replied, "I am in Tripoli, any chance you coming this way? Need any help? I'm staying a while, but not sure how long. I don't plan to die a martyr!"

That e-mail says a lot about Marie, particularly regarding her warmth as a friend and colleague. Thinking about the last sentence today, I realized the dreadful truth: Marie had indeed died as a martyr. She meant it ironically at the time, of course, but Marie, among all the foreign correspondents I've met, had a precisely defined, lifelong mission to report on the suffering she witnessed in countless conflicts and dirty wars.

Along with the French photographer Remi Ochlik, she was killed in the most dangerous place on the planet for journalists right now. She died because she wanted the world to know the full extent of the barbarism practiced by President Bashar al-Assad's forces against his own people. Her editor had ordered her out of the country, but she stayed.

So, yes, "martyr" is the right word—a martyr for truth and the standards of civilization.

The following comes from her final dispatches yesterday, from what she called the "ground zero" of the Syrian massacres:

"The Syrians are not allowing civilians to leave. Anyone who gets on the street, if they are not hit by a shell, they are sniped. There are snipers all around … I think the sickening thing is the complete merciless nature … The scale of it is just shocking."

That's all you need to know about what is going on in Syria, which is why the house where she and the other journalists sheltered was targeted by Assad's forces today. She conveyed the terror she witnessed in the calmest possible manner, and at the heart of her report was her concern for the ordinary civilian victims—as it so often was.

There is a good reason why Marie was held to be a cut above the average foreign correspondent, brave though they all are. It was her astonishingly brave behavior in East Timor in 1999, when she alone among 23 journalists refused to leave a compound where some 1,500 women and children had sought refuge from Indonesian forces. Because the soldiers knew she was still there with the unarmed U.N. force—and would tell the world if the compound was attacked—those women and children lived to be evacuated a few days later.

I often talked to her about that decision, and she said there had been absolutely no question in her mind about what she should do. It didn't occur to her to leave with all her colleagues, though she felt a little sick in the stomach as she watched the trucks disappear.

A few years earlier, I sat next to her at lecture given by the New York Times journalist David Rohde, who, when working for The Christian Science Monitor in 1995, discovered incontestable evidence of the massacres in the Bosnian enclave of Srebrenica, where Bosnian Serbs murdered 9,000 men and boys. There was only one other journalist I knew who was capable of Rohde's courage and persistence, and I was sitting next to her.

But she paid for this dedication with the loss of an eye in Sri Lanka to a hand-grenade explosion, an injury that was followed by a serious bout of post-traumatic stress disorder. It is worth mentioning that she received the unstinting support of the head of News International, Rupert Murdoch, through both. He flew her to New York to see if her eye could be saved, and during what was essentially a nervous breakdown, The Sunday Times paid for all her treatment.

What was striking about that period was her complete absence of self-pity. I never heard Marie complain about the hardships she endured or the effects of witnessing so much pain. When she was suffering from PTSD, she used to be let out of the clinic and would come round to dinner with her friend Jane Wellesley. My teenage daughters were open-mouthed at the sight of this astonishing woman with an eye patch, listening to her describe what she had done in the previous 20 years. The point, she emphasized with a tipsy flourish of cigarette and wine glass, was that women could do anything they chose. She had no children of her own, but she was wonderful at talking to kids because she treated them as equals.

Colvin was born in East Norwich, New York, near the swishy Gold Coast of Long Island (where the book The Great Gatsby is set). She carried with her, even into war zones, a little bit of that glamour. Somehow the eye patch only added to her graceful poise. But no matter how much time she spent abroad, she always remained honestly and sensibly an American.

I first met her in the mid-80s when we sat opposite each other at The Sunday Times. With a tangle of brown hair and a ready smile, she looked like a college student, but she had already covered the massacres at the Shatila and Sabra camps in Lebanon and she was by then one of the few journalists that Yasser Arafat and Colonel Gaddafi would talk to.

She lived in a flat that was let to her by our colleague David Blundy, who was later killed by a sniper's bullet in El Salvador. They shared integrity but also a rare form of glamour that stayed with Marie until she died. At parties she was always among the most dramatically dressed, and she shone with good humor and the love of her friends, of which there were hundreds.

But she was no Amazon warrior: she could love and be hurt as easily as the next person. She made me cry with laughter with the story of her late arrival to cover Kosovo and being billeted with two journalists, whose possessions she recognized in the room. Suddenly the dangers of Kosovo receded as she considered how to handle an ex-boyfriend and former husband in the same bedroom.

This evening the news from Homs has been silenced. We don't know how many people have been killed or what areas of the town are under bombardment—and that is because one of the bravest people ever to file a story is dead, and can no longer be there to bear witness.