In early 1730, Queen Sophia Dorothea attempted to orchestrate a dual marriage of Frederick and his sister
Wilhelmina with
Amelia and
Frederick, the children of King
George II of Great Britain. Fearing an alliance between Prussia and Great Britain, Field Marshal von Seckendorff, the
Austrian ambassador in Berlin, bribed Field Marshal von Grumbkow and Benjamin Reichenbach, the Prussian Minister of War and Prussian ambassador in London, respectively. The pair discreetly slandered the British and Prussian courts in the eyes of the two kings. Angered by the idea of the effete Frederick ascending the British throne, Frederick William presented impossible demands to the British, such as Prussia acquiring
Jülich and
Berg, leading to the collapse of the marriage proposal.
Frederick found an ally in his sister, Wilhelmina, with whom he remained close for life. At age 16, Frederick had formed an attachment to the king's 17-year-old page, Peter Karl Christoph Keith. Wilhelmina recorded that the two "soon became inseparable. Keith was intelligent, but without education. He served my brother from feelings of real devotion, and kept him informed of all the king's actions."
When he was 18, Frederick plotted to flee to
England with
Hans Hermann von Katte and other junior army officers. While the royal retinue was near
Mannheim in the
Electoral Palatinate, Robert Keith, Peter's brother, had an attack of conscience when the conspirators were preparing to escape and begged Frederick William for forgiveness on
August 5 1730; Frederick and Katte were subsequently arrested and imprisoned in
Küstrin. Because they were army officers who had tried to flee Prussia for
Great Britain, Frederick William leveled an accusation of treason against the pair. The king threatened the crown prince with the death penalty, then considered forcing Frederick to renounce the succession in favor of his brother,
Augustus William, although either option would have been difficult to justify to the
Reichstag of the
Holy Roman Empire. The king forced Frederick to watch the
decapitation of his friend Katte at Küstrin on
November 6.
Frederick was granted a royal pardon and released from his cell on
November 18, although he remained stripped of his military rank. Instead of returning to Berlin, however, he was forced to remain in Küstrin and began rigorous schooling in statecraft and administration for the War and Estates Departments on
November 20. Tensions eased slightly when Frederick William visited Küstrin a year later, and Frederick was allowed to visit Berlin on the occasion of his sister
Wilhelmina's marriage to Margrave
Frederick of
Bayreuth on
November 20 1731. The crown prince returned to Berlin after finally being released from his tutelage at Küstrin on
26 February 1732.
Frederick William considered marrying Frederick to
Elisabeth of Mecklenburg-Schwerin, the niece of
Empress Anna of Russia, but this plan was ardently opposed by
Prince Eugene of Savoy. Frederick himself proposed marrying
Maria Theresa of Austria in return for renouncing the succession. Instead, Eugene persuaded Frederick William, through Seckendorff, that the crown prince should marry
Elisabeth Christine of Brunswick-Bevern, a Protestant relative of the Imperial
Habsburgs. Although Frederick wrote to his sister that, "There can be neither love nor friendship between us," and he considered suicide, he went along with the wedding on
June 12, 1733. Once Frederick secured the throne in 1740, he prevented Elisabeth from visiting his court in Potsdam, granting her instead
Schönhausen Palace and apartments at the
Berliner Stadtschloss. Frederick bestowed the title of the heir to the throne, "Prince of Prussia", on his brother
Augustus William; despite this, his wife remained devoted to him.
Frederick was restored to the
Prussian Army as Colonel of the Regiment von der Goltz, stationed near
Nauen and
Neuruppin. When Prussia provided a contingent of troops to aid Austria during the
War of the Polish Succession, Frederick studied under
Prince Eugene of Savoy during the campaign against
France on the
Rhine. Frederick William, weakened by
gout brought about by the campaign, granted Frederick
Schloss Rheinsberg in
Rheinsberg, north of Neuruppin. In Rheinsberg, Frederick assembled a small number of musicians, actors and other artists. He spent his time reading, watching dramatic plays, making and listening to music, and regarded this time as one of the happiest of his life.
The works of
Niccolò Machiavelli, such as
The Prince, were considered a guideline for the behavior of a king in Frederick's age. In 1739, Frederick finished his
Anti-Machiavel — an idealistic writing in which he opposes Machiavelli. It was published
anonymously in 1740, but Voltaire distributed it in
Amsterdam to great popularity. Frederick's years dedicated to the arts instead of politics ended upon the death of Frederick William and his inheritance of the Kingdom of Prussia.