History is so tangled up in the present that it has forgotten the past Fashions may come and go but history must not forget the past must stop the struggles and return to the pastkilling time

Be it granted to me to behold you again in dying,

Hills of home! and to hear again the call;

Hear again about the graves of the martyrs the peewees crying,

And hear no more at all.

When Robert Louis Stevenson wrote those lines, he was thinking about a place I know well. The battlefield of Rullion Green lies on the northward slope of the Pentland hills, the smoke and spires of Edinburgh visible in the distance below. Here in 1666 a band of Covenanters was annihilated by well-armed soldiery. They were country people, Presbyterian fanatics, who had ridden out of the west in a desperate attempt to seize Scotland for the Lord of Hosts.

Their graves and a monument stand on the hillside. All over Lowland Scotland there are martyrs' graves where Covenanters died in the bitter decades that followed Rullion Green: the "Killing Time". Some were killed in battle; most were shot or hanged in cold blood by the dragoons who terrorised the south-west of Scotland. The Covenanters followed their ministers into the hills, worshipping in armed "conventicles" in the open air.

This is why their monuments and graves are usually in lonely places where the dragoons surprised the martyrs, on hillsides scoured by clean wind and smelling of bog-myrtle. They are remote and hard to find, which is why the Saltire Society in Edinburgh has just brought out a book by Thorbjorn Campbell, Standing Witnesses, as a guide for adventurous walkers who want to visit them.

There are two kinds of history here. There is the story of the martyrs, but there is also the story of their story: the cult of their memory. At first it was the survivors - the "savoury remnant" - who put up the stones. Then, 100 years later, came Robert Paterson, an old country stonemason who devoted his life to riding about the hills and caring for the graves, setting them straight and re-cutting weathered inscriptions. (He was the model for Sir Walter Scott's "Old Mortality".) Finally, in the mid-19th century, the memory of the Covenanters was built into the myth of the Free Church, the radical Presbyterians who broke away from the established Church of Scotland in 1843. Once again, the stones were renewed and "proper" monuments - obelisks within iron railings - installed on the battlefields.

It may sound strange, but Campbell's modest book is right at the cutting- edge of European thought about history. Its narrative is touching, and useful in a practical way. But its method is state-of-the-art French brainwork, a giddy whiff from the Sorbonne. This is a history of sites and their commemoration. As such, it fits into the debate set off by Pierre Nora with his work Lieux de Memoire (Sites of Memory).

Nora is fascinated by the new concept of "heritage", which assembles fragments of the past into displays which are entertaining and convincing to the present. But he is not concerned with whether heritage shows are "sound history". For him, they are a form of history themselves. Nora wants to examine who assembled them and why.

He is almost saying that the past cannot be recovered; all we have to play with is the ways in which the past is commemorated. We do not have the martyrs, but we have the Martyrs' Graves. We cannot recover anything much from the battle of Culloden, 250 years ago, but we do have the Clan monuments put up by later generations and we do have the Inverness Courier for 1846 which describes in detail how the battle was commemorated on its first centenary.

This is only the last somersault in the argument about "how do you write history?" which has been going on for 200 years. In the periodical Annales, the French thinker Francois Hartog has tried to work out a sequence of these fashions in history-writing.

The traditional idea, inherited from Greece and Rome, was that the past helps you to predict and form the future. Chateaubriand wrote in 1796 that he intended "to hold the torch of past revolutions in his hand to illuminate the night of future revolutions". This was replaced by the 19th century idea that "the future illuminates the past"; in other words, that scientific theory (for example Marxism) could establish once and for all what happened in history and why. This arrogant claim survived, although increasingly challenged, until after the Second World War. Then, according to Hartog, came "Presentism".

He quotes TS Eliot, who wrote about "a new kind of provincialism ... not of space but of time", in which "the world is the property solely of the living, a property in which the dead hold no shares". The past lost its rights. In 1968, students wrote "Forget the Future!" on walls. Hartog describes a present which "generates, almost from one day to the next, the past and the future which it daily needs".

This is a wonderful description of Thatcher's Britain in the 1980s, brattishly inventing a history core curriculum to legitimate Tory policies. Another rich mine of Presentist nonsense is the attempt to make history politically correct by distorting the past of non-European cultures. "Afrocentrist science", at its maddest, has suggested that ancient African science built flying machines in dynastic Egypt. The well-meaning authors of the "US National History Standard" propose to teach a history in which Europeans, Africans and native Americans all collaborated to prepare the Declaration of Independence.

But now Presentism is losing its nerve, according to Hartog. The public demands "roots" and sites of "heritage". Governments, in response, lurch from one pompous commemoration to the next. Museums that recently threw out chronology and rearranged their exhibits to show "themes" (technologies, power, religion) are having doubts. This is an age of renewed nationalism. Perhaps the old cultural-historical approach which answered for visitors the question of "how did we become the nation we are today?" was not so absurd after all.

Today history is in flux. Sarcastically, Hartog observes that the past has become unpredictable. History has disintegrated into a post-modern chaos of struggling interpretations. As Hartog puts it, "the past is ... a meadow that one crosses, intersecting the tracks of all kinds of other pasts which once had possible futures; some began to exist, while others were intercepted and massacred".

It's a terrifying image. The histories which once seemed so strong and confident now wander through the long grass, killing other histories or being killed by them. They have lost touch with the past, and they use "heritage" as a rite which may persuade the past to return and reveal itself.

It isn't the past, but the act of remembering the past which now lures the historian. The stones are there, on the windy moors, and it's true that the only thing they say for sure is that somebody cared enough to put them there. "Here Lyes John Smith Who Was Shot By Col. Buchan And The Laird Of Lee For His Adherence To The Word Of God And Scotland's Covenanted Work Of Reformation".

But in the end this minimal history will prove too timid for ordinary people. They want to grieve for John Smith, to know and hate his killers, to try at least to understand his passions. What I like about Thorbjorn Campbell is that he is not just Pierre Nora but Old Mortality too, because he is bringing us a story about human beings in their Killing Time as well as their graves. And this is a responsibility which historians cannot escape. Give us those who come to bury Caesar - but give us Caesar too.