It was Voltaire. This great man had now entered upon the final, and by far the most important, period of his astonishing career. It is a curious fact that if Voltaire had died at the age of sixty he would now only be remembered as a writer of talent and versatility, who had given conspicuous evidence, in one or two works, of a liberal and brilliant intelligence, but who had enjoyed a reputation in his own age, as a poet and dramatist, infinitely beyond his deserts. He entered upon the really significant period of his activity at an age when most men have already sought repose. Nor was this all; for, by a singular stroke of fortune, his existence was prolonged far beyond the common span; so that, in spite of the late hour of its beginning, the most fruitful and important epoch of his life extended over a quarter of a century (1754-78). That he ever entered upon this last period of his career seems in itself to have depended as much on accident as his fateful residence in England. After the publication of the _Lettres Philosophiques_, he had done very little to fulfil the promise of that work. He had retired to the country house of Madame du Châtelet, where he had devoted himself to science, play-writing, and the preparation of a universal history. His reputation had increased; for it was in these years that he produced his most popular tragedies--_Zaïre, Mérope, Alzire_, and _Mahomet_--while a correspondence carried on in the most affectionate terms with Frederick the Great yet further added to his prestige; but his essential genius still remained quiescent. Then at last Madame du Châtelet died and Voltaire took the great step of his life. At the invitation of Frederick he left France, and went to live as a pensioner of the Prussian king in the palace at Potsdam. But his stay there did not last long. It seemed as if the two most remarkable men in Europe liked each other so well that they could not remain apart--and so ill that they could not remain together. After a year or two, there was the inevitable explosion. Voltaire fled from Prussia, giving to the world before he did so one of the most amusing _jeux d'esprit_ ever written--the celebrated _Diatribe du Docteur Akakia_--and, after some hesitation, settled down near the Lake of Geneva. A few years later he moved into the _château_ of Ferney, which became henceforward his permanent abode.