On July 10, 1750, Voltaire arrived in Potsdam. He had decided to accept a long standing invitation to grace the Prussian court, and see for himself what kind of man this Philosopher-King really was. Frederick had long admired him and his ideas about the age of reason. Voltaire hated cruelty and intolerance, "my trade" he said "is to say what I think". What he thought was put in writing and amounted to an extensive library, which was purchased after his death by the Empress Catherine II and brought to St. Petersburg. Voltaire was not only an esteemed guest at Sans Souci, he was a paid companion and language teacher. Frederick usually stingy with every Pfennig, paid him well: 4000 Talers reimbursement for travel expenses, 5000 Talers as salary and free living quarters. Voltaire was overwhelmed by the hospitality shown to him by the Prussian King. His first letter to France was full of praise for Frederick. It was written with some calculation. He wanted to show France, where he had been twice imprisoned for his outspokenness, :" look here, so well was I received in Prussia, this is how a great King treats me."

For several months Voltaire was at the center of society in Potsdam and Berlin. Frederick considered him a personal friend, and where ever the King was, Voltaire could be found close by. Then came the time that Voltaire was involved in a scandal about some profit he hoped to make in a deal with a jeweler, who felt cheated and laid a charge against Voltaire. The case went to court, and all of Berlin was buzzing. The whole affair upset Frederick, who wrote a letter to Voltaire, advising him to learn from his mistakes. The tone of the letter was not that of a close friend, but still Voltaire stayed another two years in Potsdam. Other disagreements between the two men occurred at that time and at the end of March 1753 Voltaire left Potsdam. Frederick had asked him to return the poems he had written, as they were not for publication. When Voltaire left without returning them, Frederick had him stopped in Frankfurt, where he was kept several weeks under house arrest, until the missing poems were recovered. It was a sad end to the friendship of two of history's most interesting men. Some time later they took up corresponding with each other again, but they never recaptured the pleasure of their earlier friendship.