The collection came first. Rudolf gathered paintings, automata, clocks, mineral specimens, narwhal tusks sold as unicorn horn, mandrake roots, astronomical instruments and a bezoar stone in a set of rooms at Prague Castle arranged not as a hoard but as an argument: that the natural and the made world could be laid out in an order that revealed the correspondences running through them. That premise, that everything above answers to something below, is the working assumption of Renaissance natural magic, and the collection was its physical form.
The people followed the premise. Tycho Brahe came in 1599 as imperial mathematician, bringing the most accurate positional observations ever taken and an assistant, Johannes Kepler, who succeeded him in 1601 and did the work on the orbit of Mars in Prague that produced the first two of his laws of planetary motion. Both men also cast horoscopes, which was part of the post and not a lapse from it. Alchemists worked in the castle and in laboratories in the town, including Michael Maier, whose emblem books are among the central documents of the alchemical tradition.
John Dee and Edward Kelley reached Prague in 1584 with a different offer: transcripts of conversations they said they had held with angels through a scrying stone, containing a language and a revelation. They were received, and Dee presented an apocalyptic message. The papal nuncio pressed for their removal, and they were eventually expelled from imperial territory, though Kelley returned, worked for a Bohemian nobleman, and died a prisoner after failing to produce gold. The records those two men kept became, three centuries later, the foundation of Enochian magic in the Victorian occult revival.