Even today the final scene of Mervyn LeRoy's bleak 1932 prison drama, I am a Fugitive from a Chain Gang, remains one of American cinema's great moments. A wrongly imprisoned war veteran (finely played by Paul Muni) is driven ever downwards by an uncaring society and a brutal prison system. On the run, he emerges briefly to let his lover know that he is still alive. "How do you live?", she asks, and as Muni's haunted face recedes into the surrounding shadows and we hear his footsteps hurrying away, his hissed reply hangs in the air: "I steal". The irony is heartfelt. The system that he fought to protect has finally contrived to turn him into the thief that he never was.

That such a simple scene shot over 70 years ago should still have this power is, of course, a tribute to the craft of its makers: to the tightness of the writing; to Muni's extraordinarily expressive face; to the deeply resonant cinematic shadows into which he vanishes. But it also draws heavily on the metaphorical and dramatic resources provided by that prison setting, and the success of I am a Fugitive from a Chain Gang effectively founded a whole tradition of prison movies.

Not so much a fully formed genre, however, like the horror movie or the Western, as a loosely related set of character types, rhetorical tropes, and nascent themes, through which the social tenor of their times could be articulated. In the early 1930s, when even Warner Brothers felt able to embrace a social reformist agenda, I am a Fugitive from a Chain Gang and the same year's 20,000 Years in Sing Sing mounted a sustained critique of the American penal system, contributing powerfully to the growing climate of public concern with prison reform.

From then until the late 1940s prison settings offered film–makers a fertile tension between authoritarian power and individual resistance, typically expressed in the application of 'brute force'. In Dassin's 1947 film of that title, absolute power is personified, as so often, in the archetypal figure of the sadistic warder — definitively played here by Hume Cronyn. Significantly, it is his death which comes to be more important to the escapers than their own freedom.

This personification of the abstract contradiction between power and individual resistance increasingly sits at the heart of the prison movie, displacing more overt social concerns. It is already happening by 1954 in Siegel's remarkable Riot in Cell Block 11, where the tentative alliance between Dunn the violent individualist (his file describes him as a psychopath) and the reforming warden is frustrated by the bureaucrats who renege on the warden's promises. Social criticism is still present, then, but it is half submerged in the dynamics of strong men in conflict. Individualism has become the central theme.

And individualism, of course, is always ripe for romantic treatment in Hollywood, which is precisely what it receives in the best known post–war prison movie — Cool Hand Luke (1967). Making good use of Paul Newman's undoubted charisma, the film gives us a 'natural' rebel. Imprisoned for drunkenly beheading a row of parking meters — splendid symbols of petty authoritarianism — once inside, Luke's constant rebellion rewards us with empathic pleasures of identification. And even though he is killed, he lives on like a true romantic hero in the mythology which attaches to his name and in the stories passed down to subsequent generations of prisoners.

It is this kind of romanticism that increasingly undermines the social critique articulated in the classic American prison movie. Take, for example, The Shawshank Redemption (1996). For all its explicit brutality and corrupt officials, the movie's determinedly upbeat ending (the two unlikely 'buddies' re–united on the Pacific coast of Mexico) resorts unnecessarily to the 'feel–good effect': redemption nurtured in the most unlikely of circumstances. It's not that The Shawshank Redemption is an exercise in bad faith. On the contrary, it is both moving and intelligent, and is distinguished by fine performances from Tim Robbins and, especially, Morgan Freeman. But it does displace the prison movie's critical potential onto what is almost a metaphysical plane — a move subsequently made to grotesque symbolic effect in the same director's overblown death–row allegory, The Green Mile (1999).

Unsurprisingly, then, the only recent prison movie to restore social issues to their central place is not American at all, but Brazilian. It is Hector Babenco's currently released Carandiru (2003), an account of the circumstances which led to the 1992 massacre of 111 prisoners in São Paulo's notoriously overcrowded jail. To his credit, Babenco resists the temptation to lean on the standard character types. There is, for example, no sadistic warder (in fact, there are hardly any warders) and much of the film is devoted to the 'back–stories' of various inmates — the powerful, the powerless, and the simply desperate. The result is a richly textured prison movie which grips throughout, embraces a clear social agenda, and is elegantly constructed in classical cinematic style. It is a more than welcome return to the critical spirit of I am a Fugitive from a Chain Gang and to a socially aware cinema which also entertains — a quality that Hollywood seems to have lost.