Tom Holland is the author of Rubicon: The triumph and tragedy of the Roman republicand Persian fire: The first world empire, battle for the West. He describes the world in which Antony and Cleopatra takes place.

"Had Cleopatra's nose been shorter," thought the French philosopher Blaise Pascal, "The whole look of the world would have changed." 

Not, on the face of it, the most fortunate of assertions: for Cleopatra, far from being the beauty of legend, seems, judging by the portraits on her coins, to have had a nose that could hardly have been any longer. Yet Pascal's broader point, that Cleopatra's attractiveness served to shape the course of history, was nevertheless well made. Beaky she may have been, but Cleopatra could still draw on resources of seductiveness that appear to have been limitless. 

"Her sex appeal," swooned the Greek biographer Plutarch, "Together with the charm of her conversation, and the charisma evident in everything she said or did, made her, quite simply, irresistible." And who, looking at her track-record, could possibly doubt it?

Certainly, she set her sights high. So far as we know, she only ever took two lovers - both of whom, at the time, ranked as the world's most powerful man. Her favours could hardly have been more exclusive. Power, for Cleopatra, was the only aphrodisiac. This was what enabled her - long nose or no - to shape and shake her times. Only fitting, as Shakespeare's Charmian might have put it, "For a princess / Descended of so many royal kings." 

Cleopatra was doubly a monarch. As Queen of Egypt, she laid claim to the venerable title of pharaoh: not merely a devotee of the country's fabulously ancient gods, she ranked as one herself. Yet Cleopatra, although worshipped as the New Isis by her native subjects, was in fact a Greek: the heir to a dynasty originally founded by Ptolemy, a general of Alexander the Great. The Ptolemies, over the centuries, had been unfailingly characterised by viciousness, sensuality and greed - and yet their kingdom, thoughout it all, had remained illumined by the glory of the conquering Macedonian.

Alexander's tomb still stood talisman-like in the city he had laid out amid sand and marshes some 300 years before, and which was now the most dazzling urban landscape on the planet, the ultimate cosmopolis, where East and West truly met: Alexandria. No wonder that Cleopatra, growing up in such a place, dared to imagine herself successor to the legacy of the man who had founded it: the rule, not merely of Egypt, but of all the world.

An imperious fantasy - and a dangerous one. The glory of the Ptolemies, and of the whole Greek world, was much diminished from its former greatness. Indeed, of all the independent kingdoms that had been established amid the fracturing of Alexander's empire, only Egypt still retained her independence. The rest had succumbed to the expansionary ambitions of a new power, a republic, and sternly contemptous of monarchs: Rome. That the Ptolemies themselves were permitted to survive was a reflection not of their strength, but rather of their pitiful weakness. Egypt was a land of unrivalled fertility and the Roman general who conquered Alexandria would have the bread-basket of the Mediterranean in his hands. By unwritten consent, a prize so dazzling was a prize too far. In the view of most Romans, it was safer and just as profitable to leave the Ptolemies to administer the costs of their own exploitation. A succession of Cleopatra's forebears had played the role of the Republic's poodle to perfection: secure enough to squeeze their subjects dry on behalf of their patrons, impotent enough never to present the slightest threat to Rome. On such a humiliating basis were they permitted to limp along.

By the mid-1st Century BC, however, the Republic was starting to implode, and the shock-waves, inevitably, were soon reverberating throughout Alexandria. In 49 BC, Rome's greatest general, Julius Caesar, launched a civil war that would ultimately result in his establishing a dictatorship amid the rubble of his city's ancient constitution - and give Cleopatra her first stab at restoring her family's fortunes. When Caesar arrived in Alexandria in 48 BC, he quickly found himself embroiled in a dynastic death-struggle between the 21 year old queen and her younger brother. Cleopatra acted with typical decisiveness. First she had herself smuggled into Caesar's presence rolled up in a carpet; then she got herself pregnant by him; finally, with her brother defeated and killed, and herself securely upon Egypt's throne, she followed Caesar to Rome. The whole city was agog. It was said that Caesar planned to move the seat of empire to Alexandria, that he planned to marry Cleopatra, that he aimed to proclaim her the mistress of the world. Then, on the Ides of March, 44 BC, all such speculation was bloodily silenced. Caesar was assassinated. His murderers proclaimed the restoration of the Republic. Cleopatra, sensing that this was no time for her to linger in Rome, hot-footed it back home.

And there, as the Roman world succumbed to a renewed spasm of civil war, she remained. Caesar's assassins, unable to win Italy for their cause, also fled to the East. Meanwhile, Rome herself was placed under martial law by a triumvirate of the three most prominent Caesarians: Mark Antony, a playboy general who combined flamboyant vulgarity with a no less flamboyant élan; Marcus Lepidus, who had served the murdered dictator as his official deputy; and a 20 year-old, the young Octavian, Caesar's great-nephew and adopted heir. 

In 42 BC, Antony and Octavian together won a great battle outside the Macedonian city of Philippi, destroying the army of Caesar's assassins, and effectively securing the entire Roman empire for themselves. The two victors, sidelining Lepidus to a sinecure in Africa, portioned it up. Octavian, returning to Rome, received the West. Although this gave him mastery of the capital, it was also somewhat of a poisoned chalice. Italy was in turmoil. Sextus Pompeius, son of the man who had led the armies of the Republic against Julius Caesar, had profited from the chaos of the times to establish himself as the master of Sicily, and the admiral of 250 ships. Preying on the shipping lanes, he began to throttle Rome. Inevitably, the more the Romans starved, the more unpopular Octavian became.

Meanwhile, in the East, Antony was having a far more pleasurable time of it. His indulgences were those that had long been traditional among the Republic's proconsuls: fighting the Iranian kingdom of Parthia, Rome's only surviving major enemy in the East, and patronising Rome's subordinates. In 41 BC, he summoned Cleopatra to his headquarters - an unconscionable humiliation. The Queen of Egypt, however, wafting into the harbour amid the flashing of silver oars and the cooing of her attendants, had magnificently turned the tables. She knew Antony of old - vulgar, carnal, ambitious - and had correctly calculated that the best way to win his heart was with overblown spectacle. Just as he had been intended to do, Antony speedily made Cleopatra his mistress and passed a delightful winter with her in Alexandria. As with Caesar, so now with the new master of the Roman world, Cleopatra soon got herself pregnant. Having delivered Caesar a son, she went one better, and gave her new lover twins. It began to be whispered among Antony's enemies - and even his followers - that he was going native. And this is the moment at which Shakespeare's play begins…