Exeter College's rector is embarking on a journey to visit graves of Exonians killed in Great War

Together with the college's chaplain Rev Andrew Allen, Frances Carincross is spending 10 days visiting as many as possible of the "lost boys", leaving each a sprig of rosemary from the college gardens, tied in ribbon in the college colours of magenta and black

Lest we forget: Frances tending a grave (Frances Cairncross)

A century ago, Exeter College, Oxford accepted about 50 new students a year. In 1914, one of them was 17-year-old Cosmo Duff-Gordon, a nephew of the cad who had fought his way on to one of the Titanic's lifeboats. Before he matriculated, Cosmo took part in a quite different fight, and now he lies in a quiet cemetery in Northern France, along with 3,000 or so other British and Commonwealth soldiers.

I visited Cosmo's grave today, together with that of another Exonian in the same cemetery, as part of a journey to visit as many as possible of the graves of Exonians killed in the First World War. Of 771 who saw active service, 143 were killed, 113 of them on the Western Front. Their mortality rate, of 18 per cent, was the Oxford average, much higher than the national average, mainly because so many of these young men swiftly became lieutenants or second lieutenants.

Together with the Rev Andrew Allen, our college chaplain, I am spending 10 days visiting as many as possible of these "lost boys", leaving each a sprig of rosemary from the college gardens, tied in ribbon in the college colours of magenta and black. Earlier, we went to the vast Lutyens monument at Thiepval. Its ominous walls record the names of a dozen Exonians whose bodies were never found, many of them lost in the dreadful month of July 1916, when the Battle of the Somme took 10 Exonian lives.

In every cemetery we visit – tended with care by the Commonwealth War Graves Commission – the graves are watched over by the creation of another Exonian: the dramatic "Sword of Sacrifice", designed by the architect Sir Reginald Blomfield. In 1914, he had been discussing with students a redecoration of their common room; at the end of the war, he designed the great brass memorial plate in the college chapel on which so many of their names were to be recorded.

Why our visit? This year, the college has been celebrating its 700th anniversary, but this is also a reminder that the last such festivities, in the summer of 1914, took place six weeks before the declaration of war. Our undergraduate JRR Tolkien, who came up in 1911, survived three months of the Somme before a bout of trench fever saved him from further fighting. (Tubby Clayton, an earlier Exonian, also survived the war to create the famous Toc H.) Tolkien's year had Exeter's highest mortality rate: 23 of the 59 students died. Among them was Harry Allpass, a good friend, brilliant mind and budding poet, who is commemorated at Thiepval, as is Robert Gordon, a Scots scholar; Michael Windle, the son of a Liverpool vicar, died at Loos.

Even today, an Oxford college is a small and intimate institution. In 1914, it must have felt even more like a close family. RR Marett, a don who was later to be rector (college head), wrote: "In our individual and private no less than in our official capacities we had regarded these men almost as sons." Lewis Farnell, who became rector just before the war, had a breakdown in 1916 as news of the losses poured in relentlessly.

Something of this family feeling underpins our journey. Our Roll of Honour was compiled by Bob Malpass, our former building manager; our itinerary has been planned by a recent student, Tom Painter; and many of our alumni are visiting Exonian war graves in Britain and abroad which we have not had time to see. On the other hand, there is no record of the college staff who must have had their own losses. We hope to raise the funds to install a plaque for these anonymous dead beside Blomfield's memorial.

It is precisely because a college still has so many characteristics of a large family that a pilgrimage such as this is possible; and in honouring these young men, we reinforce the sense that the college's many generations are still bound together through the years.

Follow the journey at exetercollegewargraves.com and on Twitter @Rector2014