They corresponded prodigiously and effusively for four years. One wrote to "my Apollo", "my Socrates", the other to "my Trajan"; they enclosed their latest poems and swapped compliments accordingly. At last, in September 1740, the French playwright/poet/ philosophe Francois-Marie Arouet, adopted name Voltaire, aged 45, was to meet Frederick, newly crowned king of Prussia, 28. Plans were laid; expectancy soared. "I am sure to faint from joy," wrote Voltaire. Responded Frederick, "I believe I shall die from it."

The meeting would appear doomed to anticlimax, but, on the contrary, Frederick staged it well, and Voltaire was a practiced actor.

Travelling incognito westward, Frederick fell ill with the four-day ague. He send word shifting the rendezvous site to Moyland Castle, near Cleves (thereby avoiding Voltaire's mistress, the Marquise du Chatelet) and urging Voltaire to take a fast coach the 150 miles there. At Moyland, Voltaire found the king wrapped in a coarse blue dressing gown, lying on a narrow bed in a room sparsely furnished. Voltaire gave a courtly bow, Frederick a royal shiver. Superbly solicitous, Voltaire took the king's pulse, which so revived Frederick that he was able to get up, dress, dine and discourse at majestic length on free will and the immortality of the soul.

After three days, they parted. Voltaire, persecuted in France, twice took up residence at the Prussian court. His second sojourn lasted more than two years, and the relationship barely survived. Frederick still wrote poetry, but had no qualms about plunging Europe into war.

In time the philosopher king was found to have a despotic bent. Voltaire concluded that the best of all possible worlds was seriously flawed; besides, there were no women at court. He engaged in a shady financial transaction, spied a bit on the side, poked fun at the king's poems, drank too much chocolate. His departure was manoeuvred without either man's losing face, but the two were careful never to meet again