In his efforts to understand the universe, Rudolf cast a wide net. He collected pretty much everything: plants, animals, books, gems, art, and not least of all people to help discern the patterns and hidden meanings in his holdings. Rudolf beckoned physicians, mathematicians, and magicians to move to Prague. He looked to them to unspool the wisdom of Paracelsus, Pythagoras, and ancient Egyptians; reveal the Cabalist meanings of Hebrew letters; and develop new excavation techniques for his imperial mines.

Over long, boozy dinners, he heard debates about the viability of a heliocentric cosmos, a theory then still hotly contested, as it would be for another century. Tycho Brahe, the celebrated Danish stargazer whom Rudolf tapped as imperial counselor in 1599, offered an inventive take: the other planets indeed orbited the sun, Brahe said, but that entire constellation revolved around Earth.

Rudolf was intrigued by such topics, but more so by astrology, which he turned to for insights into his ongoing war with the Ottoman Turks. He bankrolled an observatory to support Brahe’s research and help him cast better astrological charts, including for Rudolf’s pet lion, Mohammed. It held great meaning for Rudolf when Brahe noted their charts were nearly identical.

In that era, astrology and astronomy were intertwined; natural philosophers sought to understand the occult forces behind magnetism and poisons while magicians tried to master them. It was a world where plants might talk, seers might speak with angels, and divine scripts might channel the power of the heavens.

And it was a time when artists could transform the mundane into the exalted, like alchemists transmuting base metal to gold. Strolling alongside his pet lion—it only occasionally mauled anybody—Rudolf wandered through the workshops of court artists, whom he commissioned to create an encyclopedia of the rare plants in his gardens and animals in his menagerie, parrots, pelicans, cheetahs, tigers, and elk among them.

Rudolf tinkered alongside his silversmiths as they fashioned symbol-rich emblems and celestial globes, including one showing the heavenly movements of Jupiter, the planet and mighty Roman god with whom the emperor identified. His dabbling in alchemical labs proved a hazard, however. Rudolf’s experiments were known to explode; once he set his beard ablaze. He was engrossed by it all.

But of all Rudolf’s many obsessions, the most fabled was his Kunstkammer, his chamber of art and wonders, believed the largest and finest then assembled.

“The Kunstkammer is a place for contemplation, a place for learning about things,” says Thomas DaCosta Kaufmann, a professor at Princeton University and author of Rudolf II: The Life and Legend of the Mad Emperor. “It also has a talismanic, magical, function—possibly. And certainly, it represents power and authority.”

No one really knows what, exactly, Rudolf’s Kunstkammer looked like or the full extent of its holdings. Records are incomplete, and he opened it to so very few. One ambassador complained he had to wait in Prague nine months to finally see it.

Royals and dignitaries given access to the multi-room, two-story wing first passed through hallways lined with paintings by Dürer, Brueghel, and da Vinci, and works depicting Rudolf as a valiant warrior, even though he hadn’t once fought on a battlefield. Upon entering the Kunstkammer, they took in the vaulted ceiling, where Jupiter guarded over Rudolf’s aggregation of some 10,000 artifacts and natural specimens drawn from far corners of the world.

“For Rudolf, as for every other collector, the Kunstkammer was a way to learn about the ‘secrets’ of God’s creation,” says Corinna Gannon, assistant curator at Germany’s Städel Museum in Frankfurt. “By possessing specimens of every realm in nature, one symbolically wielded control over the cosmos.”

A six-foot-high horn, said to be from a unicorn, towered over stuffed iguanas and flamingos. Cupboards brimmed with gems, shells, fossils, human-shaped mandrake roots, and bezoars—stone-like obstructions from animal innards believed to impart protective powers.

Mystical items abounded: a miniature, leaden devil, said to have been cast out during an exorcism; magic mirrors for scrying; talismanic handbells inscribed with Arabic, Greek, and Hebrew to ring during alchemical rituals; the fabled Codex Gigas, or “Devil’s Bible,” sat among strange tomes holding spells and incantations to summon angels or wake the dead.

The rooms were choked with mechanical wonders—astrolabes and sextants, elaborate timepieces, and automata, including a self-flagellating saint and a walking peacock that honked and fanned its feathers.

Rudolf kept adding to the collection—he was notorious for “borrowing” and never returning items from royals and monasteries—assembling an ever-fuller theater of the world.

The emperor wasn’t the first to build one of these secretive spaces. By 1565 cabinets of curiosities were growing so numerous and unruly that scholar Samuel Quiccheberg wrote a guide, Inscriptiones, advising ambitious princes to organize their own “ample theater that houses exemplary objects and exceptional images of the entire world” into natural (naturalia) and manmade (artificialia) groupings, with subdivisions therein. But Rudolf popularized the concept like no other, his collection having a “trickle-down effect,” says Evans.

Wealthy collectors across Europe paid heed to décor, staggering their displays’ heights, employing color codes, placing contrasting pieces in staged “conversations.” Like Rudolf, they sent out agents to hunt down desired items or ordered them through the Fugger family’s international trade network, that day’s amazon.com for the rich. Socially, they played their holdings for prestige, wanting them to be talked about, but granting entry to few.

The veil of secrecy that hung over cabinets of curiosities, however, was soon pierced. As more professors, physicians, and apothecaries started collecting, cabinets became not only spaces for contemplation, but also places of study, hands-on observation, and experimentation, where scholars and natural philosophers were welcomed. The Italian peninsula was a hotbed for these early “museos,” which emphasized botanical specimens. “Medicine and the powers attributed to plants are central to these,” says Evans.

The apothecary Ferrante Imperato in Naples was the first without noble standing to make his name from collecting. In 1599 he shot to fame when he published Dell’historia naturale, a massive catalog with nearly 800 pages of observations about his “theater of nature” and an eye-catching frontispiece showing a crocodile hanging from a ceiling and walls spangled with starfish. It was the first time a cabinet of curiosities was widely seen.

Swarms of nobles and scholars showed up at Imperato’s door asking to explore the plants, rocks, and creatures stashed throughout the museo, which also served as his dispensary and dissection lab. Members of the society Accademia dei Lincei, whose roster included Galileo and equally renowned polymath Giambattista della Porta, often poked through his 12,000-item collection conducting research.

Writing in 2004, biologists at the University of Naples were so impressed with the exacting nature of Imperato’s work, they declared that the apothecary “gave rise to modern zoology based on the analogical method and on experimental research.” Imperato catalogued seven unknown species of amphibians and reptiles, they noted, while meticulously dispelling a number of myths, including the long-held belief that toadstones, believed to neutralize poisons, grew in toads’ heads under the full moon. (In fact, the button-shaped stones were the fossilized teeth of a Mesozoic fish.)

Imperato’s son Francesco kept the museo open for decades after his father’s death and republished an updated edition of his book in 1672. But sometime after Francesco died, the collection disappeared.

In northern Italy, Ulisse Aldrovandi (1522–1605) took the use of images further. The first professor of natural history at the University of Bologna, he employed four full-time artists to capture his dazzling array of 18,000 items, including a whale skeleton, shark heads, stuffed storks, lodestones, barks from the West, aromatics from the East, serpents, marine monsters, botanical medicines, foreign birds, even insects. Beyond occasional donations of specimens from nobles, including the Medicis in Florence, Aldrovandi assembled his museo through an extensive international trading network of naturalists, who sent him animals, plants, and seeds.

 “Studio Aldrovandi” was frequented by scholars and students, but for those who couldn’t make it to Bologna, Aldrovandi could send detailed watercolors. He commissioned thousands of images, which he hoped to publish in the most comprehensive encyclopedia of nature ever known. According to Stanford University historian Paula Findlen, author of Possessing Nature, Aldrovandi wrote 400 volumes to that end. It was a daunting undertaking, both in terms of labor and finances. He was constantly asking for money. Only four volumes saw the printing presses before his death in 1605, though nine more were eventually published.

While occasionally fanciful—one volume devotes itself to monsters and mythological creatures—his Historia naturalis proved influential. Carl Linnaeus is said to have dubbed Aldrovandi the father of natural history, and he used the Italian’s encyclopedia as one source for Systema naturae, which introduced a groundbreaking system of taxonomy.

Through the 1600s, cabinets of curiosities sprouted up across the Italian peninsula, in Verona, Bologna, Florence, and Rome. Book after book documented their contents. Meanwhile, scholarship grounded in cabinets of curiosities also poured out of Prague and other parts of Europe. Rudolf’s physician, Anselmus de Boodt, published Gemmarum et lapidum historia (The History of Gems and Stones) in 1609. Illustrated with specimens from the imperial Kunstkammer, it was the most detailed mineralogical encyclopedia then written.

By that time, Rudolf had added early telescopes to his expanding collection. The emperor was the first to put the device into the hands of his imperial mathematician Johannes Kepler, says Kaufmann, and prompted his book Dioptrics, about how lenses work. (Kepler’s most important work, New Astronomy, which showed that planets move in elliptical orbits, was also written in Prague and was dedicated to Rudolf II when published in 1609.)Through books, letters, and in person, cabinets of curiosities created bonds among Europe’s learned men and the wealthy patrons who funded their studies. “They become a node, a place where people who are interested in the natural world come together,” says James Voelkel, a historian at the Science History Institute. And they spawned international networks for discussing findings and fallacies.

Take, for instance, the unicorn horn. Though nobody had ever captured a unicorn, their horns were frequent sights in collections. Ground into a powder, they were believed to be an antidote to any poison. Ole Worm (1588–1654), a professor of medicine and physician to the Danish king, however, dug a grave for the fabled creature. Although his museo initially held such a specimen, he was skeptical. Coming across the skull of a narwhal, a type of whale, he deduced that the sea mammal’s tusk was, in fact, what traders were hawking as unicorn horns.

Upon learning of Worm’s discovery, the king asked his physician to keep quiet, says Anne Katrine Gjerløff, a historian at the Natural History Museum of Denmark. The reason: the king’s throne, a source of great prestige. “Imagine having a throne made of unicorn horns,” she says, “and some guy comes along and says it’s just made of whale.”

Worm (pronounced Vorm) also used his collection to conduct experiments that dispelled the idea that lemmings spontaneously generated; he did so by dissecting a pregnant specimen and discovering fetuses. These efforts aside, Worm’s focus was the medicinal uses of plants, animals, and minerals, Gjerløff says, and he welcomed students from far and wide to study his holdings. The posthumous release of his handsomely illustrated compendium of the collection, Museum wormianum, finally revealed the truth about unicorns and stoked further interest in museos.

The fervor for collecting spread east. Czar Peter the Great was so moved by the cabinets of curiosities he found on a visit to Holland in 1697 that he started Russia’s first museum, the Kunstkamera.

Amsterdam was awash with unusual natural specimens plucked from the Spice Islands in today’s Indonesia and other colonial holdings. But nothing captured the czar’s imagination like Frederik Ruysch’s collection. An anatomist, Ruysch was particularly interested in fetuses, using his specimens to experiment with new preserving techniques—some using wax, others using animal blood; some he displayed pickled in jars, others he embalmed and arranged in eerie tableaux decorated with flowers and lace.

The Russian monarch was so moved by what he saw that not only did he eventually buy up Ruysch’s collection to fill his new museum, upon returning to St. Petersburg, he also ordered that anatomically deformed stillborns and deceased infants be sent to the capital for study. Physiologist Casper Friedrich Wolff used the fetuses to demonstrate “epigenesis,” the observation that embryos develop through distinct phases and are not fully formed in miniature at conception, which was the dominant idea of the time. In doing so, he laid the early foundations for embryology.

Meanwhile, in Western Europe and Britain, the arrival of microscopes made collecting small things, particularly insects, all the rage; beetles and spiders began creeping into displays. By then cabinets of natural curiosities were becoming de rigueur for early scientific societies. When Robert Hooke was admitted to the Royal Society in 1663, he was so adamant the group possess what he called a “repository” that he volunteered to fill it himself.

Simultaneously, collections started appearing in less buttoned-down settings, such as in pubs, where common folk would pay entry fees to view natural and unnatural curiosities alike—à la Ripley’s Believe It or Not. An early example was staged by the Tradescants, a former gardener to nobles and his son, who opened a popular South London museum, the Ark, around 1634. The Tradescants paired unusual plants, animal heads, and the skeleton of a whale with the hand of a mermaid, the thighbone of a giant, the feather of a phoenix, and the image of Jesus carved in a plum pit. The public ate it up.

The proliferation of these places of amusement led some scholars to draw distinctions about what made for a proper collection and who should use it. Many shunned marvel-filled cabinets of curiosities that attracted wide-eyed families and school groups.

“The use of such a collection is not for divertisement and wonder and gazing . . . like pictures for children to admire and be pleased with,” Hooke argued, “but for the most serious and diligent study of the most able and proficient in natural philosophy.”

Despite such lofty intentions, the Royal Society’s repository was initially stocked with a collection from London’s Mitre Tavern. And while it was indeed the site of scholarly study, the repository was written up in tourist guides and became a popular stop for travelers visiting London. Equally intriguing for visitors was the collection that sprawled across the home of physician Hans Sloane, who became the society’s president in 1727, succeeding Isaac Newton.

“It was a private collection during his lifetime, but he opened it up to his friends, acquaintances, and scholars,” says Dr. Alicia Hughes, project curator of the digital Sloane Lab at the British Museum. “It had quite a reputation in the early 18th century as a place that, if you were visiting London you should see.”

Sloane began collecting decades earlier in Jamaica, where he attended the island’s English governor while writing an illustrated natural history, tapping insights of planters and enslaved Africans in collecting and preserving local fauna and flora. Returning to London, he grew his collection diligently.

“He categorized, organized, and cataloged his collection quite systematically,” says Hughes. It was “always intended to be a useful collection for the production of knowledge.”

Like his royal predecessors, Sloane expanded his collection by acquiring others, some bequeathed to him. And his holdings were equally wide-ranging, including herbaria of pressed plants; African drums and “strum strumps” (banjos); engraved Persian amulets; and Chinese woodblock prints. Predictably, it also included a vast assortment of substances for his medical practice. Sloane’s pharmacopoeia held a moss-covered human skull, beaver glands, goat blood, deer hearts, boars’ teeth, silkworm cocoons, purgative roots, and even a mummified finger, according to Rutgers University historian James Delbourgo, author of Collecting the World.

As his collection swelled, Sloane worried about its future. Oxford University’s Ashmolean Museum had absorbed the Tradescants’ holdings when it opened in 1683, charging an entry fee. Sloane instead bequeathed his collection to the British government on the condition it open a free museum for “satisfying the desires of the curious” when he died in 1753. The British Museum opened six years later, showcasing only a fraction of the whopping 71,000 objects Sloane had amassed (including books).

Storage soon proved an issue, particularly of the preserved animals. According to Delbourgo, the museum’s staff eventually burned many taxidermy items because they were stinking up the place. Later, parts of the collections were diverted to the Natural History Museum, opened in 1881, and the British Library in 1973.

Despite that division, Sloane’s collection is exceptional because most of it still exists. Many collections may still be moldering away in attics and basements; others were probably tossed. Some of Aldrovandi’s ended up at the University of Bologna, but much of it was dispersed. A large part of Worm’s collection was likewise lost. As for the famed Kunstkammer of Rudolf II, who died in 1612, three days after his lion, that collection largely disappeared as well, plundered by Swedes during the Thirty Years’ War and divvied up among the country’s royals. Most of what remains is displayed at Vienna’s Kunsthistorisches Museum.

Derided by rationalists trumpeting Enlightenment science, cabinets of curiosities had largely lost their cachet by the 1800s, when formal museums of natural history took their place. Even though embryology had been drawn from them, and Linnaeus pulled from their illustrated catalogs, and early geologist Nicolas Steno relied on their holdings, Enlightenment thinkers were happy to delete cabinets of curiosities from scientific memory. These followers of Newton scoffed at Wunderkammern for the alchemical, magical, and religious ideas woven into them.

“They thought, ‘We can’t take this as serious science because it’s irrational. It’s magic,’ ” says Gjerløff. She says Worm, for example, “was discredited because he believed in alchemy.” Rudolf was an eccentric clown, and little had come out of his era, it was said. The collectors and experimenters were largely excised from history, as were their cabinets.

This neglect persisted well into the 20th century, and widespread appreciation was slow to come. Isaac Newton was exposed as an alchemist after economist John Maynard Keynes bought up his papers at auction in 1936. But it took two generations for scholars to take seriously his notebooks on alchemy, a topic long denigrated as woo-woo. Austrian art historian Julius Von Schlosser reopened forgotten Renaissance cabinets with a 1908 book, but it took until 2021 for an English translation to appear, edited and prefaced by Thomas DaCosta Kaufmann. By then younger generations of historians were viewing scientific inquiries in the context of their times and underscoring the early modern period’s importance to science’s development.

“Kepler’s laws, developments in physics—especially optics, catoptrics, and mechanics—astronomy, chemistry, biology, gemology, and ultimately space travel, they all come out of this time,” says Kaufmann.

Renewed interest in early science has led to the unearthing of some tantalizing remnants of Renaissance collections. A stash of paintings found in Windsor Castle in the 1980s revealed that King George III’s agents snatched up illustrations from early Italian museos. In 2009 botanical researchers discovered albums of dried plants at the University of Naples showing 170 “strikingly different,” unstudied specimens. They ultimately concluded the plants were from Imperato’s long-lost herbarium from the 17th century. And in 2017, a curator at Amsterdam’s Rijksmuseum stumbled across the 12 folios of paintings that comprised Rudolf II’s commissioned encyclopedia, Historia naturalis.

Now, cabinets of curiosities are popping up in museums and galleries everywhere, including a new exhibition at the Louvre this spring on nature and art in the court of Rudolf II.

Meanwhile, a new generation is trying its hand at assembling Wunderkammern. Filmmaker Wes Anderson and author Juman Malouf curated an exhibition in Vienna based on the theme in 2018; installations by Lebanese artist Ali Cherri made a splash at Art Basel Paris in October; and New York’s Fashion Institute of Technology just opened a show.

As we navigate the upheavals of a new age of discovery, one probing frontiers that are equally distant and hard to grasp—deep space, artificial intelligence, mirror life—perhaps it’s only natural we turn back to collecting and ordering things to exercise a bit of control on our small corners of the world.