A European collector has paid $750,000 (£400,000) for 26 letters sent by the French philosopher Voltaire to the Russian Empress Catherine the Great.
Some of the letters are signed "The old hermit"
The figure is a world record for handwritten correspondence from this period, said Sotheby's auction house.
The 26 letters date from 1768-1777, when Catherine was ruler of Russia and Voltaire lived in Switzerland.
Some of the letters are signed "the old hermit" while in others the philosopher simply refers to himself as "V".
Catherine II, also known as Catherine the Great, was a German-born Empress who ruled Russia from 1762-96.
She described herself as a "philosopher on the throne" and corresponded with several prominent European thinkers throughout her reign.
The letters from Voltaire discuss her foreign policy, including the partition of Poland and her first war with the Ottoman Empire in 1768-74.
The Ottoman ruler, Mustafa III, comes in for ridicule throughout the correspondence, with Voltaire referring to him as "fat and ignorant".
The collection far exceeded its estimated price of $385,000 (£205,000).
A first edition of James Joyce's Ulysses also sold for $148,000 (£79,000) at the auction in Paris.