In his new book Graham Robb takes a journey through the 'Debatable Land', a small but crucial missing part in the history of England and Scotland. Here, Graham explains how his fascination began, and explains exactly what, and where, the ‘Debatable Land’ is.

Early one evening in the autumn of 2010, my wife Margaret and I stood in front of Carlisle railway station in the far north-west of England with two loaded bicycles and a one-way ticket from Oxford. After twenty-three years in the South, we had decided to move to Scotland. The idea was to live closer to my mother, her son and daughter-in-law becoming every day a more distant memory. By chance, our search had ended just short of the border, at a lonely house on the very edge of England.

During our last months in Oxford, I had read about our future home and discovered that the river which almost surrounds the house had once marked the southern boundary of a region called the Debatable Land. For several centuries, this desolate tract running north-east from the Solway Firth had served as a buffer between the two nations. Within those fifty square miles, by parliamentary decrees issued by both countries in 1537 and 1551, ‘all Englishmen and Scottishmen are and shall be free to rob, burn, spoil, slay, murder and destroy, all and every such person and persons, their bodies, property, goods and livestock . . . without any redress to be made for same’. By all accounts, they availed themselves of the privilege. Under Henry VIII, Elizabeth I, James V and James VI, the Debatable Land had been the bloodiest region in Britain. Fifty years later, when most of its population was slaughtered or deported, it became the last part of Great Britain to be conquered and brought under the control of a state.

The Debatable Land – a name it acquired in the last two centuries of its existence – is the oldest detectable territorial division in Great Britain. Its roots lie in an age when neither England nor Scotland nor even the Roman Empire could be imagined. Today, though some of its boundaries survive as sections of the national border, it has vanished from the map and no one knows exactly where and what it was.

From its northernmost point, one thousand feet above sea level, to the great estuary into which all its becks, burns, gills, sikes and waters flow, the Debatable Land measures only thirteen miles. The widest crossing is eight and a half miles, and it can be circumambulated – with difficulty – in two days. There are three ranges of hills, one mountain and, when the tide is in, a mile of coastline. A main artery of the British road system passes through it, yet it is quite possible to spend a long day walking across it without seeing another human being, even in the distance.

I had no idea how much there was to be explored and no intention of writing a book about the place in which we had found a home. Then, under the powerful spell of idle curiosity, documents and maps arrived unbidden: the land and its inhabitants seemed to have become aware that someone was taking an interest in them. The story unfolded itself between 2010 and 2016, and the independent territory which used to exist between Scotland and England began to look like a crucial, missing piece in the puzzle of British history.