The Red Wedding grabbed all the headlines, but for me the most haunting moment in the last season of Game of Thrones came a few episodes earlier, as one of Westeros's most machiavellian political operators – Petyr Baelish, royal Master of Coin, brothel-keeper and self-made-man extraordinaire – describes the brutal game at which he so excels. "Chaos isn't a pit. Chaos is a ladder. Many who try to climb it fail, and never get to try again. The fall breaks them. And some are given a chance to climb, but they refuse. They cling to the realm, or the gods, or love: illusions. Only the ladder is real; the climb is all there is."

It might appear, looking at Westeros and the medieval past from which so much of its inspiration is drawn, that the ladder is built for men. The wearing of skirts, not to mention the frequent necessity of taking them off, keeps women from competing in the climb. As William Caxton wrote in his 1474 translation of The Game and Play of the Chess – a book for which he could easily have chosen the title Game of Thrones – "it is not fitting nor seemly thing for a woman to go to battle for the fragility and feebleness of her". The theory is simple: men rule, and women don't.

It takes only a moment, though, to see that the reality is more complex. In any kingdom, where the right to rule is inherited by blood, there's a risk that the crown will come to rest on a female head. Daenerys Stormborn is the last survivor of House Targaryen, determined to make good her dynastic right to the Iron Throne – just as Matilda, granddaughter of the Conqueror and only surviving legitimate child of King Henry I, claimed the crown of England on her father's death in 1135. Like Matilda, Daenerys is implacable in pursuit of her birthright but, like Matilda, she's compromised by the fact that she can't lead her own troops into battle. It took 20 years of civil war in 12th-century England before Matilda's claim was vindicated in the person of her son, who took the throne in her place as King Henry II. We don't yet know if Daenerys will establish a woman's right to rule in Westeros, but if she does, it will also be thanks to her role as a mother – metaphorically, rather than literally – of the fearsome dragons who are both her ultimate weapon and fire-breathing proof of her innate royal authority.

Still, Matilda and Daenerys are the exceptions. For most women born into the political world, their job description is more pawn than queen: to serve as the physical embodiment of political alliances by marrying husbands chosen by their fathers and giving birth to male heirs. As so often in Game of Thrones, the brave-hearted Starks of Winterfell show us how it should be done. "Your father didn't love me when we married," matriarch Catelyn points out to her eldest son, Robb. "He hardly knew me, or I him. Love didn't just happen to us. We built it slowly over the years, stone by stone, for you, for your brothers and sisters, for all of us. It's not as exciting as secret passion in the woods, but it is stronger. It lasts longer." She could be describing the devoted and fruitful relationship of England's heroic King Edward III and his loyal wife Philippa of Hainault, who married as teenagers amid a snowstorm under the unfinished roof of York Minster – a Winterfell wedding if ever there was one.

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But Robb, the young King in the North, doesn't listen to his mother's advice. He marries for love, breaking a solemn oath and a military alliance as he does so – and the massacre of his family at the Red Wedding is the result. The young Yorkist King Edward IV's impetuous union with the beautiful Elizabeth Woodville didn't produce such an immediate bloodbath in 15th-century England, but its eventual consequences – dead princes in the Tower, a usurping king slaughtered at Bosworth and the coming of the Tudors – were scarcely less cataclysmic: the Plantagenets, like the Starks, wiped out by their enemies.

Catelyn Stark's sage counsel, however, is a sign that noble wives are more than brood mares. Female power might most often be soft power, exercised through behind-the-scenes influence on husbands and sons, but it is power all the same. Lady Olenna, the grande dame of up-and-coming House Tyrell, is the most fearlessly formidable player yet to appear in the snake-pit of Westeros's capital. She also irresistibly echoes the 15th-century duchess of Suffolk, Alice Chaucer, granddaughter of the poet, and the single most able politician, for my money, to stalk the corridors of power on either side during the long and bloody Wars of the Roses.

In Olenna's own indefatigably perky granddaughter Margaery, shortly to marry the loathsome King Joffrey Baratheon, the old lady has a talented apprentice; but at court there is a cautionary tale for the future Queen Margaery in the unhappy person of the Queen Mother, Cersei Lannister. Cersei initially seems an adept in the dangerous power-play that surrounds her. Like Isabella of France, the "she-wolf" who deposed and murdered her husband, Edward II, before ruling in the name of her young son, Edward III, Cersei plots to dispose of her despised husband, King Robert Baratheon, in order to become the power behind the throne of her son Joffrey. But now, caught between her sadistic bully of a son and her pitiless bully of a father, she is a bitter and thwarted figure, rarely seen without a goblet of anaesthetising wine clutched in her elegant hand.

It remains to be seen which way the forced marriage of the beleaguered Sansa Stark to Cersei's brother Tyrion will go, but the younger Stark girl, Arya, has chosen a different path: with her iron will, her cropped hair and her boy's clothes, she is becoming a distinctively charismatic figure – albeit one driven by revenge rather than faith, and much keener on killing than that iconic female warrior, Joan of Arc. For Arya and the similarly transgressive Brienne of Tarth, though, the stifling conventions of a woman's place in the Seven Kingdoms offer none of the freedoms, military, social or sexual, enjoyed by the wildling fighter Ygritte among the tribes of the Free Folk north of the Wall.

All the same, the women of Westeros with noble blood in their veins have choices that aren't available to those at the bottom of the social pile. Sex sells, and what's true for HBO's ratings is true too for Westeros's women who start with nothing: Tyrion's mistress Shae, the mysterious priestess Melisandre, the prostitute Ros who runs Lord Baelish's brothel. Unclothed female bodies offer a route up the ladder, just as armed male bodies do for the mercenary "sellswords", who seek their fortune by fighting.

History tends to record only the names of those who make it to the top – and what's true for men is doubly so for women. But this imagined universe can give the climb a human face, and remind us that its risks are terrifying. Ros has brains and beauty, and she's come a long way from a whorehouse in Winterfell, but she misses her footing when she tries to double-cross her powerful employer. As Baelish's curling voice describes the fate of those who fall, we see Ros, limp and empty-eyed, hanging by her hands from the royal bed, her body pierced with bolts shot from the crossbow of the psychopathic Joffrey. Lashings of sex and violence, and a shockingly unpredictable narrative rush: not just a way to pull in the viewers, but a chilling experience of the precariousness of life in a brutal historical world.

Helen Castor's new history of Joan of Arc will be published in October. Game of Thrones is on Sky Atlantic from Monday 7 April.