Cleopatra dallied with Romans from Julius Caesar to Mark Antony to save her skin and fabulous lifestyle. For scarcely less pressing reasons, at least of political exigency, her male forebears in the Ptolemaic dynasty felt forced into bed with their sisters to secure their power base as foreign occupiers on the Nile by an untroubled succession.

No particular proclivity for "pushing the prong into forbidden fleshpots" - to quote a Ptolemaic poet who paid for such frankness with his life - led to Ptolemy II marrying his bossy elder sister Arsinoe II in 274 BC, says Greek scholar Costas Buraselis. At an international conference at Auckland University July 13-16 focused on Ptolemy II's reign in Alexandria (282-46), Buraselis, professor of ancient history at Athens University, ascribed the incestuous union resulting in Ptolemy III to political savvy.

"To Greeks it was strange and improper," he said. "Greek public opinion distanced itself from the practice." His research, however, has revealed half a dozen cases of full sibling marriage, with issue, among pharaohs in the second millennium BC, then several round the turn of the millennium - "altogether not a negligible set of sibling marriages."

Ptolemy II is known to posterity as Ptolemy II Philadelphus (sister lover), so the fact of his four-year marriage lasting till Arsinoe's death in 270 seems to have been central to his identity. Buraselis argues the union helped to elevate the status of the invader rulers from northern Greece who annexed territory conquered by Alexander the Great. To the Egyptian populace, royal sibling marriage would have seemed modelled on the practice of ancient divinities, and Arsinoe became a cult figure, a deified queen.

Astutely engendered Ptolemaic power structure - and military muscle - facilitated burgeoning of a Greek metropolis in Egypt that for a critical 200 years or so was the centre of the ancient world. A score of top scholars of the period from major universities worldwide vied with each other to analyse factors that made this early Alexandria so legendary.

Oswyn Murray of Balliol College, Oxford, was magisterial: with aptly suave Alexandrian elegance, he indicated how patronage from Philadelphus led to a thriving, if fatally elitist cultural life centred on the new library and museum or temple of the muses. Reliant on royal goodwill, literary talent of the era "hugged the shore and fluttered wings against the ground" - to quote a Sturm und Dranger literary figure C.G. Heyne - never rising to the sublime heights of the free spirits of democratic classical Athens. "But Alexandria was unique in the ancient world, unlike any city in the world today, except perhaps London," he said.

About 100,000 Jews were believed to be among its multi-ethnic citizenry, some with not much Hebrew, so translation of their ancient religious literature into contemporary Greek - koine - was no less important than cleaning up versions of the Homeric epics in circulation.

Greeks in fact created the chronology of the Hebrew scriptures as they were translated into Greek by 70 or so scholars brought from Jerusalem for the job, asserted French-born, Swiss resident Philippe Guillauime of the Near East School of Theology at Beirut (who put himself up at a city backpackers' hostel for the privilege of attending the event). His novel account of the Septuagint translation raised eyebrows, but his insight into Semitic mentality earned judicious respect.

Guest speaker at the conference, which was run by the university classics and ancient history department, was maverick British Marxist Martin Bernal, author of the controversial Black Athena (1987). Little loved in academia - and less in Greece - for debunking the Greekness of ancient Greece in favour of what he alleged was "massive" input from the Semitic world, Bernal gained no new followers from his Antipodean campus lectures. (He did admit to being deliberately somewhat obfuscating though). His opinion that the Macedonian takeover of Egypt in the fourth century BC was to be compared with Japanese occupation of China in Second World War was met with stony scepticism.

Greek ambassador to New Zealand Vangelis Damianakis, of Hania, Crete, and his wife, Glykeria, hosted a dinner for conference participants, complete with fine modern Greek wine, a Mantinea, of the aromatic red Moschophilero grape grown in Arkadia. A further Ptolemaic conference is proposed in two years, possibly in Germany.