In 1667, he employed as his master builder the Venetian architect Girolamo Sartorio, who designed many buildings in the town, including the Neustädter Kirche, and was instrumental in the expansion of the Herrenhausen Gardens.
In 1676, John Frederick employed Gottfried Wilhelm Leibniz as Privy Councillor and librarian of the important ducal library. Thus began Leibniz's 40-year association with the House of Hanover, which resulted in three generations of Hanovers being patrons to one of the most eminent philosophers and mathematicians of Europe.
John Frederick, c.1675, by Johann HulsmanFuneral thaler for John Frederick, 1679
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