"Power wearies those who don't have it," is a favourite aphorism of the former Italian prime minister, Giulio Andreotti, 90, whose dark and mysterious political career is brilliantly celebrated in the film Il Divo. The remark isn't in the film, but it might as well be, as it strikes to the heart of the matter.

The whole film focuses on Andreotti's obsession with power and his fear that he might lose it at any moment. The career reads - at least according to the film, which is based on real events and dialogue - as a series of interleaving plots and conspiracies, one opening into another like a nest of Chinese boxes.

From the Borgias to Berlusconi, Italy produces conspiracies and plots almost as an art form. Andreotti was always seen as the supreme schemer, organising trade-offs with the Mafia to win more than 300,000 preferential votes in Sicily alone in election after election, squaring off friends and foes in parliament, and carrying out his private foreign policy with the likes of Brezhnev and Gadaffi. At the height of his powers in the 1970s he had a patronage machine that Warwick the Kingmaker would have envied.

Andreotti became master of the politics and the state he never entirely trusted. This is the key to his career, and why conspiracy and faction flourish with such extravagance in Italy. Since the decline of the Roman emperors, the country has never been run by one undivided and trusted regime. When the Empire revived under Charlemagne, it was ruled beyond the Alps.

Italy's plight was depicted brilliantly by Dante Alighieri, one of the first to write in Italian of the "nation" of Italy. "The cities of Italy are full of tyrants, and every upstart embraces a faction to become another (dictator) Marcellus," laments the poet Sordello in Il Purgatorio. Though rich in culture, ideas and invention, Italy has lacked a credible national political narrative. Attempts to manufacture a national myth in the last century by utopian writers and artists such as D'Annunzio or Marinetti ended in the violent absurdity of Mussolini.