In August 1736, Frederick the Great, then Crown Prince of Prussia and a great admirer of Voltaire, initiated a correspondence with him. That December, Voltaire moved to Holland for two months and became acquainted with the scientists Herman Boerhaave and 's Gravesande. From mid-1739 to mid-1740 Voltaire lived largely in Brussels, at first with the Marquise, who was unsuccessfully attempting to pursue a 60-year-old family legal case regarding the ownership of two estates in Limburg. In July 1740, he traveled to the Hague on behalf of Frederick in an attempt to dissuade a dubious publisher, van Duren, from printing without permission Frederick's "Anti-Machiavel". In September Voltaire and Frederick (now King) met for the first time in Moyland Castle near Cleves and in November Voltaire was Frederick's guest in Berlin for two weeks, followed by a meeting in September 1742 at Aix-la-Chapelle. Voltaire was sent to Frederick's court in 1743 by the French government as an envoy and spy to gauge Frederick's military intentions in the War of the Austrian Succession.