The Battle of the Somme, which began in early July 1916, has come to symbolise the horror and futility of war, as Fergal Keane reflects on a visit to the battlefield.

On the other side of the wood, the fighters soared and looped in a bright blue sky.

I was standing in a cornfield and thought of how, in another time, that sound would have sent me running in terror for any cover I could find.