All you need is mud...

...and plenty of it, if you want to evoke the Middle Ages convincingly on screen. Foul disease and hideous cruelty help, too. At least, that's Chris Peachment's theory

I haven't a clue which centuries constitute the medieval age. And I am not going to do that boring journalist's thing of looking it up in the OED and giving you the definition. I imagine it is a period somewhere between the fifth and 15th centuries AD, somewhere between the collapse of the Roman Empire and the start of the Renaissance, give or take a hundred years. But it is not the dates that interest me. It is all the things that "medieval" evokes. Things such as mud. Things such as chaps in armour. Serious amounts of religion, tempered by witchcraft, and a horribly active Inquisition. Interesting diseases, especially leprosy. Proles with hideous teeth (there is a line in Tennyson's Idylls of the King about a churl who "sputters through a hedge of splintered teeth"). And, of course, unspeakable cruelty, whether on battlefields or in dungeons. I may not know much about medievalism, but I know what I like.

Braveheart (reviewed opposite) has a similar devil-may-care attitude to the period. No doubt thousands of Scottish historians will write in to show me up, but it strikes me that Mel Gibson as William Wallace, clad in a loose-weave kilt and wearing blue make-up all over his face, is placing himself somewhere around 1300. Which would surely be 500 years before the kilt was invented and 500 years after woad went out of fashion. To say nothing of his hair extensions, which must have given his medieval hair consultant awful problems. At least he ends up hanged, drawn and quartered, which is very medieval. There is also a lot of mud, but then it was filmed in Ireland.

Hollywood hasn't been very big on mud. It prefers to see the Middle Ages as a fairly clean place. Richard Thorpe's prodigious output in the early Fifties included Ivanhoe, Knights of the Round Table and The Adventures of Quentin Durward, all of them starring the very clean Robert Taylor and all of them seeing the Middle Ages not as a muddy age but as a good excuse to unfurl banners in full technicolour. Ivanhoe did have quicksand, though, which sucked up knights in armour in one quick slurp. Franklyn Schaffner's creditable The War Lord, starring Chuck Heston as the Norman chieftain, wasn't very muddy, but it did have a lot of pagan sacrifices. Errol Flynn never got his green tights dirty in Sherwood. Even the recent First Knight had Camelot looking like a Disney model village, covered in pristine white stone and roofed with electric blue tiles. As well as no mud, there was also a noticeable absence of myth, magic, Mordred and Merlin, or indeed anything from the M section of the Camelot phonebook. When Richard Gere and Julia Ormond enjoy a kiss in the rain, it is mainly to acquire that fashionable wet look, rather than to get dirty.

Mud belongs to the European tradition. There are whole faculties of Medieval History professors who hire out their services to European medieval films and insist that there be a lot of historically accurate mud. There was The Return of Martin Guerre, in which Depardieu comes back from the wars - which ones I can't remember, but they must be medieval wars, because after 10 years away no one spots that he isn't the man he claims to be. Ten medieval years can take an awful toll on a man's appearance. He duly starts rooting around in the mud, raising pigs and such-like.

There was an awful lot of mud in Tarkovsky's Andrei Rublev, too. This tale of a medieval Russian monk's long journey through incredible suffering got muddier and muddier as it went along. Monks got their eyes put out with boiling tar, churls staged orgies under Rublev's nose, all sorts of medieval outrages kept happening to the wandering mendicant, but the one sure thing was that his habit got more and more dung-coloured as he travailed on. The final episode, in which a divinely inspired boy casts a large iron bell, takes place in one huge mud pit.

Kurosawa's The Seven Samurai also ends in one of the wettest, muddiest battle scenes ever, with the Samurai doing that strange Japanese waddling run which makes them look like ducks trailing their bottoms in the mud. I don't know if it is set in the Middle Ages, but Samurai warlords are definitely feudal.

But the one truly inspired use of mud is in Monty Python and the Holy Grail. In this Camelot, the Peasants' Anarchist Collective aren't just squelching around in the mud, they are actually making mud pies, while simultaneously whingeing about being "repressed". When Arthur explains that he is king because he got Excalibur from the Lady of the Lake, the peasants' union leader replies: "Strange women in ponds is no basis for a system of government." Some of Arthur's knights are later repulsed from a French castle by great gobbets of flying brown goo. One hopes it was mud, but with the French you can never be too certain.

Monty Python was also spot on in many other respects of medievalism. Its unspeakable cruelty, for one thing. Whenever you now see a knight spouting blood through every orifice of his armour, you cannot help but hark back to John Cleese as the Guardian of the Bridge, getting his arms and legs lopped off one by one, and, finally a limbless trunk, shouting at Arthur: "Come back and fight like a man. It's only a scratch. I'll bite yer legs off."

It was unfortunate that Robert Bresson's masterpiece Lancelot du Lac happened to be released shortly after the Monty Python film. Bresson's take on the Arthurian legend stripped the tale of myth and magic and substituted a mysterious poetic atmosphere of foreboding and dread. The final battle for Camelot is unseen but for an unmounted horse galloping aimlessly through the forest, which is populated by knights staggering around with blood coursing through the seams of their armour. You can't help but recall John Cleese. Bresson is also famous for shooting much of the picture at thigh level, but he does at least give each knight colour-coded tights, so you know roughly who is who.

Not much colour-coding in In the Name of the Rose, since most of the cast are monks clad in brown sackcloth. But you can easily see that it is medieval because of the diseases. Since Sean Connery specialised in primitive medicine, there is a whole host of pestilences on display, from leprosy to the plague. Hundreds of extras sported interesting black buboes in the armpit - a sure sign of the plague. And Ron Perlman (recently in City of Lost Children) hasn't just got black stumps for teeth, he's got a hunchback as well. There were also some inventive deaths handed out by F Murray Abraham as the Grand Inquisitor.

Death personified belongs to Ingmar Bergman, of course. Mention a knight on a beach, playing chess with a cowled figure, and everyone will shout The Seventh Seal, even if they haven't seen it. There's a lot of self- flagellation in it, too, which is very medieval. The film did prompt one funny line from one of the children in Barry Levinson's Diner: "I went to Atlantic City once. But I didn't see Death on the beach."

All of these medieval elements are what the French structuralist critic Roland Barthes would have called "signifiers". He also wrote an essay claiming that the new Citroen car was the modern equivalent of Chartres Cathedral, which shows how daft French critics can be. The unlikely figure of Tarantino got it about right in Pulp Fiction, when the vengeful Marcellus tells his tormentor, now safely trussed up, "I'm gonna get medieval on yo' ass." I don't suppose Tarantino knows when the medieval age was either. But he's got the spirit of the thing.