The inscription carved into the huge beech tree, which stands on a hill path in Gloucestershire, England, reads “PM 10/9/13 MKN.”

Next month, this piece of vandalism — though I cannot see it as that now — will be 100 years old, which seems incredible for something probably done on the spur of the moment. I often wonder about PM and MKN — if their love lasted and whether both made it through World War I, which broke out 11 months later, on Aug. 4.

It seems likely that PM was a young man who dug his knife into the smooth surface of the already ancient tree, putting himself above the date and the initials of the girl of his dreams. It was a Wednesday, perhaps in the evening after they both had finished work, when this path is dappled with light from the west. I suspect they were together and that some kind of declaration or promise was made, which is why he carved the date so deep into the bark.

I can’t be sure about any of this, of course, but last week I toured four local war memorials to search for a PM, or a MKN, just in case the carver had put his initials second, and was pleased that I found neither. Perhaps both survived the war and lived happily into the 20th century.

Looking at those war memorials is shocking because of the sheer numbers. It reminded me that Aug. 4 is the anniversary of Britain’s war declaration against Germany and that next year we will mark the centenary to end all centenaries: 100 years since those boys began to leave the fields for the hell of Flanders.

Celebration of that doomed generation can be mawkish and there are justified reservations about our love of anniversaries, for example when Spitfires and a lone Lancaster bomber start appearing in the skies to mark any national triumph. But whatever the apprehension about this anniversary, how best to honor it, what lessons to take from it and whether we are being chivvied into recalling the sacrifice for possibly dubious nationalistic reasons, it will be important because World War I was the moment that humans began to realize the power of total destruction.

It is odd to think that in the first year of the Great War, the 100th anniversary of Waterloo was passed and that the British soldiers who fought at the battle of Loos in 1915 were as close to the Duke of Wellington’s “infamous, very weak and ill-equipped army” in 1815 as we are to them.

The British casualties in this single battle almost exactly equaled the 50,000 infantry that Wellington fielded at Waterloo. In 100 years of industrialization, we had learned a lot about mobilization and mass destruction. The first indiscriminate chemical weapons deployed by the British were at Loos, which followed the example of gas shells fired by the French and Germans during the previous year.

The scale of what we were prepared to do to one another was a shock and it inspired poets and artists to appalled eloquence, which, by the way, subsequently added to the aura of the doomed generation and, to some degree, distracted from the barbarity. Can an event that prods Owen, Sassoon, Graves, Remarque, Gurney and Nash into great art be completely bad? Their answer would have been yes. So the temptation to wallow in the sacrifice and heroism should be resisted, if only to keep straight in our minds what war on a continental scale would mean for us.

A centenary marks the point at which an event passes from living memory to deep history. There are no longer any World War I veterans left, although there are a few people who remember being alive during the war and plenty who knew soldiers who fought (both my grandfathers were seriously wounded serving in the same regiment on the Western Front). So this is the moment that the Great War is given over to myth and the care of historians. However seemingly enormous, its relevance to us is gradually reduced.

There are forthcoming books by Max Hastings and Anthony Seldon, and a BBC series and a book by Jeremy Paxman. In a sense, these volumes and the government’s four-year program of events, which starts with a service of Commonwealth leaders in Glasgow Cathedral on Aug. 4 next year, are closing a book.

The celebration of anniversaries like this one is a modern phenomenon. Anniversaries in the first 1,500 years of the Christian era were essentially religious feasts, owned by the church. The state did little to organize sentiment to mark a glorious event in the past. The first example I can find is Henry VIII crossing the Channel and making his way to the village of Agincourt, just short of 100 years after the English victory there.

In the last years of Tudor rule, Shakespeare celebrated the battle in his play “Henry V.” Henry’s St. Crispin’s Day speech gave to the English a notion of making a glorious sacrifice in France, as well as the need to honor it. “He that shall live this day, and see old age, will yearly on the vigil feast his neighbors and say, ‘Tomorrow is Saint Crispian.’ “

Some residue of this must have played in the minds of the members of the British Expeditionary Force of 1914.

The point of Henry V’s exhortation to honor an anniversary was to encourage sacrifice, which is perhaps where my doubts lie. I have no objection to the observance of the 30th anniversary of the Falklands war last year, as long as it’s not used to give a false account of the past, boost the desire for glory on the battlefield or give undue expectations of success in the future. One lesson from World War I is that a campaign that was going to be over by Christmas 1914 metastasized over four years to ruin the lives of millions of people and transform the world in unforeseen ways, for example the tyranny in Russia and the slide of Germany into national socialism.

I am tempted to say that anniversaries are best left to the people, but that is never going to happen and, besides, I have to concede that the state has a proper role to play. It is fine for an anniversary to give us an honest account of who we are and what we stood for as well honoring the dead, just so long as we understand that today we are probably as ignorant of the dangers of the times we live in as the lad who carved his initials on a tree 100 years ago.

That’s the big lesson we can take from next year’s centenary.

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