Ever since John Kampfner was a young journalist in Communist East Berlin, he hasn't been able to get the city out of his mind. It is a place tortured by its past, obsessed with memories, a place where traumas are unleashed and the traumatised have gathered.

Over the past four years Kampfner has walked the length and breadth of Berlin, delving into the archives, and talking to historians and writers, architects and archaeologists. He clambers onto a fallen statue of Lenin; he rummages in boxes of early Medieval bones; he learns about the cabaret star so outrageous she was thrown out of the city.

Berlin has been a military barracks, industrial powerhouse, centre of learning, hotbed of decadence - and the laboratory for the worst experiment in horror known to man. Now a city of refuge, it is home to 180 nationalities, and more than a quarter of the population has a migrant background. Berlin never stands still. It is never satisfied. But it is now the irresistible capital to which the world is gravitating.