SPOILER ALERT: This article discusses events in Game of Thrones that may spoil the viewing for those catching up on box sets.

Although Hilary Mantel is apparently yet to begin the third volume of her trilogy of novels about Thomas Cromwell, we can be confident of several plot twists that it will not feature. Cromwell will not precipitate a civil war. He will not betray the husband of his foster-sister, with whom he is in love. He will not escape the executioner's block. His downfall is scripted. The history books cannot be cheated. Mantel's Cromwell is as bound to the inevitability of his doom as any prisoner to a rack.

In the hands of a great writer, of course, the fact that we already know a character's fate can serve to heighten rather than diminish tension. For all that, though, the pleasure to be had in following a narrative and not knowing what will happen is a primal one. Next week sees the return to our television screens of a series that, like Mantel's two Tudor Booker prize winners, charts the pleasures and perils of political ambition. In a trailer for Game of Thrones, the voice of the actor Aiden Gillen can be heard defining chaos as a ladder: "The climb is all there is."

Gillen's character, Petyr Baelish, certainly knows whereof he speaks. The world he inhabits is one that will seem perfectly familiar to readers of Wolf Hall: courtly, treacherous and full of people having their heads chopped off with axes. Politics is portrayed as a game, in which only the most skilful can hope to win. Baelish himself has risen from humble beginnings to a position of understated influence and power. In the first series of Game of Thrones, he is shown serving a warrior king gone to seed and oppressed by serious marital problems. Baelish's talent is for keeping his spendthrift master in cash. "Within three years of coming to court he had been made master of coin and a member of the small council, and today the crown's revenues were 10 times what they had been under his predecessor."

If Baelish sounds more than a little like Thomas Cromwell, then perhaps that is not entirely a coincidence. He may inhabit a world, Westeros, which features dragons, walking corpses and a 700ft wall of ice – yet it is far from wholly fantastical. George RR Martin, whose series of novels inspired the HBO drama, has woven a tapestry of extraordinary size and richness; and most of the threads he has used derive from the history of our own world.

Gillen's look in the TV series, complete with black doublet and pointed beard, serves the viewer as convenient shorthand for the role he is playing in the drama: that of a Tudor Machiavel. Cromwell and Walsingham are not the only models for this. Baelish's character is inspired as well by the traditions of revenge tragedy: he has a taste for poison and nurtures a semi-incestuous passion for his foster-sister. What neither the history nor the literature of the Tudor period can reveal to us, though, is the full depth and nature of Baelish's schemings – nor, because there are still two books of the series to be written, what his fate will be.



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Adding to the impossibility of deciding where Martin may be taking the fabulously complex strands of his plot is that the world of Westeros does not draw for its inspiration on a single period of history. Baelish may seem a figure conjured from Tudor mythography, but the king who rules in the first book in fact resembles Henry VIII less than he does his grandfather: the founder of the Yorkist dynasty, Edward IV. The back story of the series certainly derives from the wars of the roses. Just as the house of Lancaster was toppled by the house of York, so, at the beginning of Game of Thrones, has the ruling dynasty of the Targaryens been toppled by a usurper, Robert Baratheon.

Again, though, it would be a mistake to imagine that Martin's purposes can be divined simply by transplanting the history of 15th-century England on to the convulsions that devastate Westeros. He is far too subtle for that. When Robert succumbs to a plot hatched by his beautiful queen, Cersei, who then rules the kingdom on behalf of her son, it is hard not to be reminded of Isabella, the wonderfully nicknamed "she-wolf of France", who similarly dealt with her own husband, Edward II. When a fleet attacks her capital only to be annihilated by liquid explosives, the obvious parallel is with the "Greek fire" deployed by the Byzantines in their defence of Constantinople against the Arabs. Different events – and different periods – elide to consistently potent and surprising effect. In Game of Thrones, episodes from the history of our own world lie in wait for the characters like booby traps.

Lena Headey as Cersei Lannister ... It's hard not to be reminded of Isabella, 'she-wolf of France'

In this, the obvious contrast is with the only work of fantasy to compare in terms of ambition and achievement to Martin's own: The Lord of the Rings. Tolkien's Middle-earth, unlike Westeros, is the creation of a dauntingly learned scholar: his ambition was to fashion from the languages, literature and history of the early middle ages an invented mythology that would nevertheless retain the stamp of the period that had inspired it. Martin's approach is infinitely more slapdash. Just as the characters and plot twists of his novels derive from a whole range of different periods, so too do their settings. The default mode is high medieval, but alongside all the tournaments and castles there are echoes as well of earlier periods. Offshore, a recognisably Viking kingdom boasts a fleet of longships; Westeros itself, like dark ages England, was once a heptarchy, a realm of seven kingdoms; the massive rampart of ice which guards its northernmost frontier is recognisably inspired by Hadrian's wall. Beyond Westeros, in a continent traversed by a Targaryen would-be queen, the echoes of our own world's history are just as clear – if more exotic. An army of horsemen sweeps across endless grasslands, much as Genghis Khan's Mongols did; memories of a vanished empire conflate Rome with the legend of Atlantis.

The result might easily have been a hideous mess. Instead, Game of Thrones is fantasy's equivalent of a perfect cocktail. Elements drawn from the hundred years war and the Italian Renaissance, from Chrétien de Troyes and Icelandic epic, fuse to seamless effect. The measure of how credible – on its own terms – people find Martin's alternative history is precisely the phenomenal scale of its popularity. The appeal of Westeros is less that it is fantastical than that it seems so richly, so vividly, so brutally real. The supernatural has no starring role: it is merely as present in the lives of its characters as a trust in the reality of angels, or a dread of demons, would have been in the minds of medieval men and women. People take their pleasures and endure their sufferings with a plausibility that puts to shame a good deal of self-proclaimed literary fiction.

Seat of power … the Throne Room in Game of Thrones

The result, paradoxically, is that there are sequences where the invented world of Westeros can seem more realistic than the evocations of the past to be found in many a historical novel. No fiction set in the 14th century, for instance, has ever rivalled the portrayal in Game of Thrones of what, for a hapless peasantry, the ambitions of rival kings were liable to mean in practice: the depredations of écorcheurs; rape and torture; the long, slow agonies of famine. The pleasures of historical fiction and of authentic, adrenaline-charged suspense, of not knowing who will triumph and who will perish, have never before been so brilliantly combined. Imagine watching a drama set in the wars of the roses, or at the court of Henry VIII, and having absolutely no idea what is due to happen. No wonder Game of Thrones has been such a success – and that historians can relish it as much as anyone.

Twitter: @holland_tom

• Game of Thrones season three begins in the US on Sunday 31 March and the UK on Monday 1 April