It was the loudest explosion I’d ever heard. I was at work in my hotel along Jalan Wahid Hasyim, a street in the center of Jakarta, when from down the road came what sounded like a huge thunderclap. But the morning sky was a steely blue, as it had been the day before and the day before that.

Had a lorry exploded? A gas tank? From my window, I couldn’t see a plume of smoke anywhere, but my modest little hotel looked out over just one small corner of the city. Jakarta, with ten million inhabitants, is a sprawling megalopolis covering almost 700 square kilometers; if you count its satellite cities, the population is no less than thirty million. Five minutes later Jeanne called, in a total panic.

It seemed so unlike her. We’d met six months earlier at a language course in Yogyakarta. She was a young French freelance journalist and one of the most relaxed travelers I had encountered.

Jeanne was based in Jakarta and, at that very moment, on her way to my hotel. We planned to spend the day visiting retirement homes in outlying districts, in search of eyewitnesses to history. She would interpret for me, as she had before.

But now she was in tears. ‘There’s been an attack! I had to run from the shooting, and I’m hiding in the mall around the corner from you!’ Out into the street. The usual endless honking traffic had been replaced by a crowd of hundreds and hundreds.

Multitudes of the city’s poor were holding up their smartphones to film the scene. Four hundred meters .