I have long been interested in landscape history, and when younger and more robust I used to do much tramping of the English landscape in search of ancient field systems, drove roads, indications of prehistoric settlement. Towns and cities, too, which always retain the ghost of their earlier incarnations beneath today's concrete and glass.

We all need a past - that's where our sense of identity comes from.

But who knows their own child? You know bits - certain predictable reactions, a handful of familiar qualities. The rest is impenetrable. And quite right too. You give birth to them. You do not design them.

It seems to me that everything that happens to us is a disconcerting mix of choice and contingency.

I didn't want it to be a book that made pronouncements.

I've always been fascinated by the operation of memory - the way in which it is not linear but fragmented, and its ambivalence.

We open our mouths and out flow words whose ancestries we do not even know. We are walking lexicons. In a single sentence of idle chatter we preserve Latin, Anglo-Saxon, Norse: we carry a museum inside our heads, each day we commemorate peoples of whom we have never heard.