However, the line's significance is arguably still greater than all that. If Durand had not produced his frontier, the conflicts that have plagued the region since the Soviet invasion of 1979 might never have occurred. 

In trying to investigate the line's unintended consequences, I spent some time in the archives at the British Library and the School of Oriental and African Studies, researching both its author and the circumstances in which he did his work. He was born near Bhopal in central India in 1850, and his background fitted him perfectly for a career as a high Imperial official. His father, Major-General Sir Henry Marion Durand, was the illegitimate son of a brother of the Duke of Northumberland, and, in the course of his own career, helped crush the 1857 Indian Mutiny with efficient brutality. When he felt it necessary, he did not shrink from burning villages that had harboured insurgents, nor from ordering prisoners to be shot in cold blood.

Thirteen years later, as governor of the Punjab, Sir Marion met a peculiar end less than 70 miles from the line his son would later draw. As he advanced on an elephant through a ceremonial arch to enter a local chieftain's garden in Tank, on the border with tribal Waziristan, his head hit the stonework, and having been thrown from his howdah, Sir Marion expired a day later.

Photographs of Mortimer taken in his prime depict a big, cold-eyed man, his cheeks hidden behind an extravagant moustache: he looks almost Prussian. Contemporaries commented on his apparent rigidity, and when, at the time of his Afghan mission, the Spectator dubbed him "the strongest man in the Empire", he professed himself delighted. Yet he also hid a surprising vulnerability. When the Mutiny broke out, Mortimer, though just seven, had been sent away to school in Switzerland. It was there that that he learnt that his pregnant mother, Annie, had died of a fever, having been forced to make a series of marches to escape the rebels who had captured the family's home at Indore. 

Perhaps it was to compensate for this loss that when Durand read for the Bar at Lincoln's Inn in his early twenties, he began a passionate affair with an older widow, a Mrs Neville. He promised her he would bring her with him when he took up his first Indian Civil Service posting in 1873, but his family, fearful his career would be ruined, was scandalised. Finally, Durand caved in, announcing his surrender in a letter to his sister Madge, his closest confidante for more than 50 years: "There is one argument in your letter which seems to me unanswerable — that of letting Mrs Neville be subject to ‘Talk'... No one knowing her would think evil of her making her home with me, but I suppose you are right. The world is hatefully malicious."