The Bacchae is a Greek tragedy with an eerie relevance in the 21st century, its star tells Arminta Wallace.

It was first performed two and a half thousand years ago: a staggering statistic, when you stop to think about it. But what's even more staggering is the visceral impact of Euripides' play The Bacchae, which is still treading the boards in 2006, this time in a new version by Conall Morrison at the Abbey Theatre. It is - even by the standards of Greek tragedy, with its fondness for lethal family get-togethers followed by a spot of indiscriminate slaughter - a shocker. The plot doesn't mess about, either. Charismatic Eastern leader arrives unexpectedly in well-ordered Western city, with devastating results. Sound familiar?

Morrison's adaptation underscores the analogy with 21st-century world politics by moving the action from ancient Thebes to the Green Zone in Baghdad - and as the actor Christopher Simpson points out, it's an uncannily accurate match. "We are living in relatively grotesque times," he says, "and the play speaks to the barbarism of fundamentalism, the savagery of extremism."

Simpson takes the role of Dionysus, the stranger who comes to the city run by his autocratic cousin Pentheus bearing a message of . . . well, what? In his spine-tingling opening speech, Dionysus declares his intention to claim his rightful place as divine - and divinely inspired - leader.

In the process, he will convert the sinful locals to his way of thinking: which, it transpires, will involve a good deal of drinking, dancing and dodgy goings-on, mostly in the mountains outside the city, and mostly involving his female followers, the bacchae of the title.

"Dionysus represents the disaffected, the alienated, the estranged," says Simpson. "He is the one who has not been accorded what he considers his legitimate right to a voice, and a place. He returns to unpack - with devastating brilliance - the might of the establishment. Pentheus represents the ideological, economic and cultural assumptions of the West; Dionysus represents an energy that is new, strange and troubling in its exoticism. The play, for me, examines the opposition of world views, and how each faction creates an ideology which seeks to eradicate the other."

The Bacchae, however, is not a simple tale of good guys versus bad guys. For a start, Dionysus and Pentheus are cousins. "The bonds they have are those of family - which makes the alienation all the greater, and the sense of hurt all the more distressing," says Simpson. "It also tells the lie of 'otherness', because the point about the idea of the 'other' is that it calls into question our sense of self. We are all others to somebody; we are all strangers somewhere."

At this level the play also explores our creation of self through language, weaving a tapestry which upends our assumptions about who "we" and "they" might actually be. Pentheus and Dionysus are, it turns out, the flip side of each other.

If this sounds acutely philosophical, that's because it is: Euripides was a close friend of Socrates, and his plays are suffused with the shrewd unravelling of unquestioned assumptions for which that philosopher is justly famous. Cool philosophical dialogue, however, is not the modus operandi of The Bacchae. Its depiction of humanity at its brutal worst is breathtaking; and it ends horrifically, with the dismemberment of one of the central characters.

"What's fascinating about this play," says Simpson, "is how there is a great sense of terror and carnage. It is, by and large, reported rather than presented on stage; and yet it's horrific. I think it is scary to have a mother rip her son apart. That's troubling."

For a 21st-century audience, it also - somehow - adds to the piece's contemporary resonance. We should, though, be wary of the presumption that we - somehow - have a direct line into these ancient texts, or indeed into the society which produced them. Two and a half thousand years later, can we really know what kind of punch Euripides intended his plays to deliver? The opinions of his contemporaries are interesting in this respect. Euripides' work was regarded with some suspicion, partly because of what we would call its realism, and partly for its focus on internal psychology.

According to the comic writer Aristophanes, Euripides lowered the tone of Greek tragedy by portraying heroes in a singularly unheroic way, and by introducing "the vulgar affairs of ordinary life" on to the stage.

Aristophanes also objected to Euripides' immorality, lack of piety, and unhealthy interest in new-fangled doctrines - such as the outlandish theory, which Euripides went out of his way to bring to his audience's attention, that the sun was not really a golden chariot steered across the sky by an elusive god, but rather "a great fiery stone".

Whether it all brings Euripides closer to our 21st-century mind-set, or simply underlines the enormous cultural differences between ancient Greece and the post-modern West, is a moot point.

Either way The Bacchae, Euripides's final play, was not performed until after his death in 405 BCE, when it took first prize at the ancient Greek equivalent of the Oscars. It is now regarded, along with Alcestis, Medea and Electra, as one of his finest surviving works - none of which has saved it from becoming the subject of what one commentator calls "an intense interpretative argument".

One way of looking at the play sees The Bacchae as a simple morality tale of divine punishment against Pentheus and Thebes for their refusal to accept Dionysus' divinity. It is also possible to argue that Dionysus embodies those atavistic aspects of human experience which have been repressed by the structured life of the city; his return may offer an opportunity to create an energising, harmonious synthesis. A third interpretation has focused on the piece as an indictment of religion, which it portrays as a breeding-ground for dangerous superstition and fanatical excess.

In the end, the most interesting reading of The Bacchae may be one which refuses to come down on one side or the other and sees it, instead, as a bleak vision of contradictions which are inescapably part of the human condition. One critic has suggested a parallel with Joseph Conrad's novel Heart of Darkness, which also contrasts two irreconcilable world views - European life, stressing political power and bureaucratic rationality, and African life, with its stress on passion and acceptance of the wildness of nature - and observes what happens when they collide. Life, Conrad concludes, is "a choice of nightmares".

Is Euripides's play really as black as that? It remains to be seen how Morrison's vision plays out on stage. "I think Conall has brought out quite carefully how versions of the truth are presented, mediated and refuted," says Christopher Simpson. "Dionysus is an apologist, an evangelist, a fundamentalist - he's many persuasive things. And while the audience may sympathise with this man who has been alienated, they may also view him as a terror. And there is something sinister about someone who will do what he must do. At all costs."

The Bacchae of Baghdad, directed by Conall Morrison, with Christopher Simpson as Dionysus, Robert O'Mahoney as Pentheus and Andrea Irvine as Agave, runs at The Abbey until April 22