It currently seems the only three that interests Hollywood relates to dimensionality. The reverence once extended to the film trilogy is fast diminishing, and although third instalments are due for Transformers, Ong-Bak, Paranormal Activity, Alvin and the Chipmunks, Men in Black, Madagascar, Batman and Iron Man, only the first two have been announced as series finales.

Indeed, with Scre4m, Pirates of the Caribbean 4: On Stranger Tides and Spy Kids 4: All the Time in the World soon to be followed by fourth entries in the Austin Powers, Mission: Impossible, Underworld and Bourne franchises, the trilogy could soon go the way of the 2D movie, as the synergy-obsessed suits controlling the multi-media conglomerates now owning the major studios adhere to the maxim that familiarity breeds both content and profit.

Reared on the original Star Wars triptych, Lord of the Rings executive producer Mark Ordesky once opined that "the worst thing you can do is inorganically try to create a trilogy when one doesn't exist". But few of his contemporaries exhibit similar qualms in commissioning additional sequels to box office hits, with stereoscopy reducing the risk (for the moment) and increasing the possibility of runaway successes such as 3D Sex and Zen: Extreme Ecstasy.

Since Ivor Novello silently essayed The Rat three times in the 1920s, the majority of movie trilogies have been accidental, with self-contained continuations involving recurring characters or themes predominating over single storylines. Indeed, while the Hollywood studio system concentrated on long-running series such as Andy Hardy and Charlie Chan, the trilogy became the preserve of European directors such as Pasolini, Saura, Wenders, Haneke and Von Trier. But even auteurs like Edgar Reitz couldn't resist adding a fourth (albeit fragmentary) part to his magisterial Heimat trilogy in 2006.

Yet while the makers of the Back to the Future, Evil Dead and Red Curtain trilogies knew when to stop, the third picture has frequently proved a step too far, most notably in the case of Fritz Lang's Dr Mabuse and Francis Ford Coppola's Godfather trines. Walden Media recently announced plans to reduce the seven instalments of Narnia to five, by skipping The Silver Chair and The Horse and His Boy. But such contractions are rare and the trilogy looks set to become a major victim of Hollywood's continuing bout of sequelitis.

The Trilogy Top 10

1) The Human Condition trilogy: No Greater Love, Road to Eternity (both 1959), A Soldier's Prayer (1961)

Running nine hours and 47 minutes, Masaki Kobayashi's pacifist masterpiece follows everyman Tatsuya Nakadai's intimately epic struggle against the Japanese militarist mentality.

2) The Apu trilogy: Pather Panchali (1955), Aparajito (1957), Apu Sansar (1959)

Establishing an Indian parallel cinema alongside the Bollywood mainstream, Satyajit Ray's Bengali triptych also had an incalculable influence on film-making across the developing world.

3) Ingmar Bergman's Chamber trilogy: Through a Glass Darkly (1961), Winter Light (1963), The Silence (1963)

An excruciating record of the Swede's struggle with his faith and the

growing realisation that there's no hope of otherworldly salvation.

4) The Three Colours trilogy: Three Colours: Blue, Three Colours: White (both 1993), Three Colours: Red (1994)

Krzysztof Kieslowski's genius for ironic ambiguity is evident in this

treatise on the French revolutionary principles of liberty, fraternity and equality.

5) Roberto Rossellini's War trilogy: Rome, Open City (1945), Paisà (1946), Germany, Year Zero (1947)

Laying the foundations for Italian neo-realism, this second world war trio retains its power, poignancy and deep compassion.

6) Michelangelo Antonioni's Alienation trilogy: L'Avventura (1960), La Notte (1961), L'Eclisse (1962)

Starring Monica Vitti and exploring the dehumanising effects of moder urban living, this has a stylistic and thematic unity that ranks it among the masterworks of auteur cinema.

7) The Toy Story trilogy: Toy Story (1995), Toy Story 2 (1999), Toy Story 3 (2010)

A rare example of a latterday trilogy that actually improves with each episode.

8) The Gorky trilogy: The Childhood of Maxim Gorky (1938), My Apprenticeship (1939), My Universities (1940)

Not to be confused with the equally fine Maxim trilogy, Mark Donskoi's adaptation of Maxim Gorky's autobiography expertly combines romanticism and humanism.

9) John Ford's Cavalry trilogy: Fort Apache (1948), She Wore a Yellow Ribbon (1949), Rio Grande (1950)

Narrowly pipping Sergio Leone's Dollars trilogy, this sums up Ford's attitudes to the West and his relationship with John Wayne.

10) The Terence Davies trilogy: Children (1976), Madonna and Child (1980), Death and Transfiguration (1983)

British cinema boasts several fine trilogies by the likes of Bill Douglas and Lindsay Anderson, but Davies's is the most powerful and cinematic.