NO-ONE was quite sure, afterwards, what John Wilkes Boothe cried as he leapt from the box, his gun discharged, that fateful night Abraham and Mary Lincoln decided to take in a show. Some insisted he shouted, ''The South is avenged!'' Most, though, said they heard him shout, ''Sic semper tyrannis,'' - ''thus always with tyrants.''

Uneasy lies the head that wears a crown. Nor, in a century that has seen despotisms of unparalleled impact - the power of wicked rulers much extended by modern technology and mass communications - has life grown any more secure for the average despot.

Suharto fell last week, driven from office after decades in ruthless charge of Indonesia. He fell because of a disintegrating economy; the great mass of his subjects for the first time facing hunger, deprivation, and uncertainty. And he fell because, at length, the mob took to the streets, in such numbers and with such fury that no force could contain them.

But Suharto fell, above all, because he lost the united support of the Army, his chief instrument of terror. All tyrannies are sustained by force. Some survive by crude, sustained warfare, army and nation always engaged in the wasting of neighbours.

Hitler dreamed of a Germany in perpetual war, the volk united in a glorious cause and the economy fuelled by European looting.

Most, though, survive in a climate of fear. Chairman Mao - who, in terms of the sheer millions who died under his capricious regime, was probably the foulest dictator of our age - kept China in obedient turmoil through violent changes of economic and social policy.

And all really good dictatorships know the subtler weapons of control. The knock on the door at night. A vast, paid, network of spies and informers. Solitary confinement. Torture, of course. The Argentine junta

specialised in ''disappearing'' people. Your neighbour vanished one night, or your brother, or your flatmate, never to be seen again.

Despotism, too, calls on a measure of largesse and showmanship. A free bread ration to the masses sustained imperial Rome for centuries, combined with free entertainments; chariot races, wild-beast shows, and so on.

And there is a monumental architecture - inherently fascist, be it Brandenburg Gates, Trajan's Column or, for that matter, the Millennium Dome - and the magnificently vulgar artforms of the despotic. One thinks of the vast banners Soviet workers used to carry in grand parades - Glory to the Workers of the Beetroot Collectives - or Leni Riefenstahl's beautiful, sweeping, utterly evil film of Nazi apotheosis at Nuremberg, The Triumph of the Will (1936).

Competent dictatorships, in the short term, make the trains run on time. They build corporate states. No aspect of national life is free from control by Big Brother. Religion is state-organised. Broadcasting and the arts are firmly controlled. The economy is planned, rigidly. The young are indoctrinated, both in school and in special youth organisations. Full employment is essential for a regime's survival. There are bread and circuses; there are chickens in every pot.

What is appalling, through decades, is the power of wicked regimes to attract support abroad. Mighty multinational corporations prize stability before democracy, and will happily deal with - even bankroll - the most unsavoury, murderous regimes. Even worse is the existence, in every age, of liberal fans and apologists.

Assorted Fabians travelled to pre-war Russia to extol Uncle Joe and the benevolent Stalinist regime. High Tories, in England, made no secret of their regard for Hitler, and enthusiastically pursued appeasement.

In our time we have that ageing communist gangster, Fidel Castro of Cuba, whose career has been sustained by murderous oppression at home and the export of mayhem overseas. Even he has had his apologists. Castro is ''steeped in democracy,'' bubbled Saul Lando. Leo Huberman and Paul Sweezy eagerly defended the ''passionate humanitarian''. Norman Mailer called him ''the first and greatest hero to appear in the world since the Second World War'', and so on.

And yet the Castro regime has quite failed. He had not been in power for five years when Cubans were fleeing by their thousands, on feet, by outboard motor. By 1980 it was reckoned a fifth of all Cubans were living abroad. By 1990 the country was generally reckoned to have the lowest standard of living in the western world, save perhaps Haiti. The Cuban community in the United States, hugely successful, generates a GDP 11 times larger than that of Cuba itself. Castro, and his wretched little state, survive as an awful warning of the useless, impoverished dogmas of Marxist-Leninism.

In the long term all despotisms fail. Rome provides powerful examples. The Julio-Claudian line founded the monarchy; but the early Caesars failed to establish a dynasty, so enthusiastically did they jail, poison, starve, exile, or throttle each other. Cousin was married to cousin in a jealous bid to keep the clan intact; the inbreeding made each generation of Caesars madder than their parents. Mighty as they were, few Caesars died of old age. Tiberius, Caligula, Claudius, Nero, Galba, Otho, Vitellius, Domitian - all met violent or poisoned deaths. Nero was the last of the old line; when he gurgled ''Qualis artifex pereo!'' no male of the Imperial House survived to succeed him.

Paranoia sustains tyranny, and

at length consumes it. The despot creates a reign of terror but in the end the terror encircles him. He cannot trust his closest lieutenant. His court bristles with potential assassins. Even his family may, at the

last, hasten his end - or prolong his sick, comatose existence for their own purposes.

General Galtieri, losing control, invaded the Falklands in a bid to unite Argentina in jingoist frenzy. He lost the war, and fell. At least he escaped with his life. The Ceausescus of Romania lived in gross splendour and at the head of a corporate state governed with psychotic control. There was no underground press, for instance: typewriters and photocopiers were illegal.

The orphans of the Securitate furnished a fanatical bodyguard. A maze of secret tunnels provided ready escape from the presidential palace. Vast sums of money were established in overseas banks. None of this saved their lives. Overthrown by the mob in December 1989, abandoned by his closest associates, Ceausescu was readily caught, put on quick mock-trial, and shot like a dog.

Awful was Stalin's end. Friends, colleagues, his own family - none was safe from his murderous sense of fun. At length, in 1953, he took his fatal stroke, and lay for hours alone and untended, all his household being too terrified to approach. So he died. His dreadful henchman, Beria, was immediately shot by the Politburo, with their own pistols.

The assassin, the rebellion, the coup, the revolution - the tyrant might, just, survive them all. But he cannot withstand the last enemy. Infirmity, old age, and death come without respect for might. There might be a state funeral; embalmed remains may be displayed upon decades. How often, though, graves have been defiled. A tyrant's head has served as a soldiers' football. Shakespeare caught it in these terrible lines:

Imperious Caesar, dead, and

turn'd to clay

Might stop a hole, and keep the

wind away . . .