Monseigneur, I would needs be insensible not to be infinitely touched by the letter with which Your Royal Highness has deigned to honour me. It has greatly flattered my sense of pride; but my love for mankind, which has always ruled my heart and which has also—dare I say it—formed my character, affords me a pleasure that is a thousand times purer when I realise that there exists in the world a prince who thinks like a man: a philosopher prince who will make man happier.
Allow me to tell you that there is not a being on earth who will not derive blessed benefits from the care that you take to cultivate sound philosophy in a soul born to command. Believe me, the only truly good kings have been those who, like you, began by acquiring knowledge, by getting to know mankind, by loving the truth and by detesting persecution and superstition. No prince who thinks like this can fail to create a golden age in his realm. Why do so few kings seek such advantages? You have sensed the reason, monseigneur, which is that almost all concern themselves more with royalty than with humanity—whilst you do precisely the contrary.
Be assured that, provided tumultuous affairs of state and human wickedness do not alter such a divine character, you will be adored by your peoples and treasured by the entire world. Philosophers worthy of the name will hasten to your domains and, just as famous artists flock to countries where their art is most appreciated, thinkers will come to gather around your throne …
The image is a detail from an engraving that purports to show Voltaire turning from his desk to converse with Frederick the Great (V did in later years accept the king's invitation to the Prussian royal court)