A rose is a rose is a rose is a rose, unless it appears in a story by Stephen King. In the ultra-prolific author’s sprawling fictional universe, a rose is a nexus of reality growing out of the ground on the corner of 46th Street and Second Avenue in Manhattan. Destroy the rose, and one destroys the Dark Tower, a spire that stands in a field of softly singing red roses on another level of reality and binds a massive multiverse together. All of which is to say that to King’s so-called “Constant Readers,” who’ve read enough of his writing to understand the symbolism, roses aren’t just romantic; they’re a matter of life and death.

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It’s completely OK, and not uncommon, to like King and not find it fitting that the bodega on the real-life 46th and Second has roses for sale. Constant Readers likely make up a minority of the enormous audience that King has cultivated over the past 45 years, a period during which his estimated lifetime count of book copies sold (more than 350 million) has easily exceeded the current population of the United States. Most of King’s work isn’t explicitly serialized and doesn’t depend on knowledge of any other entries in his catalog. A rookie reader can dip a toe in anywhere and succumb to the same narrative riptide that keeps King veterans from escaping his pull.

But King, whose every book becomes a best seller and, now more than ever, gets optioned for the screen seemingly the moment the manuscript is submitted, is as much of an outlier in the world-building department as he is in his popular success and unflagging pace of production. Because King has also created what J.R.R. Tolkien called an ambitious “secondary world,” which in King’s case started as a dark, distorted vision of the Maine he knew and grew to encompass a universe. For readers who’ve followed him closely during that decades-long construction project, a motif like the rose serves as a “super-allusion,” as Michael Collings, one of several King scholars who’ve spent much of their careers indexing and analyzing King’s work, calls it. “With a single image—for example, the red rose in an abandoned lot—he can bring into the story all of the power implicit in half a dozen other stories that share the same image,” Collings says, adding, “It gives a moment of connection, of understanding possible ways that this story might fit into its universe, justifying and clarifying actions, characters, and landscapes.”

It’s difficult, if not impossible, to pinpoint when King started consciously creating his secondary universe, and King, who at 70 is busy still speedily expanding it, declined a request to discuss its foundation. But elements of intertextuality crept into his output early. In his seventh novel, 1979’s The Dead Zone, King has a character reference “that book Carrie,” his debut novel from 1974. But Carrie and The Dead Zone don’t share a reality; in the latter book, the events of the former are fiction, just as they are in ours. But then there’s Cujo, King’s 10th novel, which came out in 1981. Like The Dead Zone, Cujo takes place in the fictional town of Castle Rock, Maine, and more than one character from the former story appears or is referenced in the latter—not as a figment from a book by Stephen King, but as a part of the town’s fictional fabric. Castle Rock has reappeared in many subsequent King works and most recently resurfaced as the setting of the ongoing, same-named Hulu anthology series, which doesn’t adapt plots from specific King works so much as it draws its aesthetic (and Easter eggs) from all of them.

Castle Rock is one of a trinity of towns that makes up most of King’s mirror Maine, along with Jerusalem’s Lot (which debuted in the 1975 novel ’Salem’s Lot) and Derry (which first appeared in a 1981 short story, “The Bird and the Album,” and went on to feature prominently in novels such as It and Insomnia). As each fictional town accumulates new narratives, it becomes more real to the reader, lending an air of authenticity to the events that occur there. For King’s Constant Readers, returning to a town like Derry or Castle Rock is like coming home again, albeit a home where the horrible happens. “You have all of these nodes, and these nodes connect to these stories,” says George Beahm, author of The Stephen King Companion and other works. “And at some point this town that we call Castle Rock reaches a critical point—a point of combustion where it literally can become alive and become consuming.”

Eventually, though, the Kingverse outgrew Maine. Like a hermit crab scavenging for a more expansive shell, he came across a home that had the dimensions he needed: Mid-World, the fantasy setting of what became his magnum opus, The Dark Tower. That series, which has its own vernacular, tells a self-contained narrative that unfolds over eight novels (and one novella) published over 30 years and in the works for more than 40, but it’s also inextricably linked with dozens of ostensibly non–Dark Tower tales, deepening their significance and, in turn, drawing depth from them. Beahm describes the fictional framework as a blank map in King’s mind. As his bibliography sprouts new stories, Beahm says, “he starts sketching in parts of that map. Finally when he writes something, then you can take a pincushion, stick it in the map and say, ‘OK, this is where this is and this is where that is,’ and everything certainly in the large sense is drawn to The Dark Tower. Everything springs out from that.”

King began writing The Gunslinger, the first book in the Dark Tower series, in 1970, although it wasn’t published as a complete entity until 1982. (In 2003, King rereleased it in a revised and expanded form.) In The Gunslinger, he introduced The Dark Tower’s protagonist, Roland Deschain, the last of a long line of peacekeepers. As the seams of his world slowly fray around him, the ancient Roland tries to reach the titular tower, the axis upon which innumerable parallel realities hinge. Along the way, he encounters Jake Chambers, a boy from 1970s New York City who slips into his world and joins him on his journey. But toward the end of the book, Roland lets Jake tumble to his (temporary) death, opting for information from his nemesis, The Man in Black, over saving his friend. As Jake falls, he says, “Go, then. There are other worlds than these,” a line that hinted at the scope of the sequels to come, which frequently reference and reintroduce King characters from outside the saga.

“That really is, I think, the starting point of the multiverse,” says Robin Furth, who worked as King’s research assistant on the series and wrote Stephen King’s The Dark Tower: A Concordance. “It was there from the very beginning.” Collings concurs, arguing that King “envisioned a sequence of interrelated novels and stories that, taken as a whole, would encompass a worldview.”

That worldview revolves around the battle between barbarism and civilization, a theme that recurs in much of King’s work. It’s also central to Lord of the Flies, a formative book for King, who borrowed the name Castle Rock from the location in Lord of the Flies that the boys who descend into savagery use as their base of operations. “It’s the idea that King has always had that evil is an infestation,” Beahm says. “It’s not only a physical infestation, as it is with Leland Gaunt coming to town [in the 1991 novel Needful Things], but it’s a moral infestation with this rotting nature that comes from within. So you have evil from within and without.”

In the later volumes of the Dark Tower series, which King wrote in a burst of mortality-fueled inspiration after he was hit by a van while walking in 1999 and almost died, he inserts himself into the story as a character who, like the real-life author, has to survive in order for the quest to reach its conclusion. That decision marks a new level of self-referential writing, but even that has antecedents in his earlier work, going back to a short story he wrote while at the University of Maine. In that recently republished story, called “The Blue Air Compressor,” King pauses the narrative so that he can step in and address the reader directly, and he’s continued that dialogue with his Constant Readers in many of his introductions to subsequent works. That’s an example of how many of King’s early tendencies, including his world-weaving, reached a fuller expression later. Bev Vincent, another author who, like Furth, has worked with King and written his own books about The Dark Tower, thinks the shared world blossomed organically from the experience of setting so many stories in Castle Rock. “He always says that he’s an intuitive writer,” Vincent says. “He doesn’t have an outline. He doesn’t have a big plan. He just sort of goes where the story takes him, and these things just happen.”

Lately, though, King has taken a more direct and intentional approach to tightening the links between his creations. “In the process of writing, an author becomes aware, ‘Aha, this is what I’m writing about. This is how I’m seeing.’ And they build it into that world,” Furth says, adding, “Especially as a mature author, [in] the last almost 20 years that I’ve known him and worked with him, he is consciously building in those ties.” That evolution leads to a different reading experience depending on when and in what order a reader discovers King’s work. For instance, the earliest incidences of a super-allusion like the number 19, which figures prominently in a pivotal scene in 1979’s The Dead Zone even though King didn’t purposefully incorporate it into his writing until after his accident (which took place on June 19, 1999), seem to take on an added significance that King didn’t intend when he wrote them—as do the moments when his readers encounter the number 19 in the wild. And character names that occur in more than one King work, like Patrick Hockstetter (It and Firestarter) and Ralph Anderson (The Outsider and Storm of the Century), in retrospect may appear to belong to the same person, or possibly “twinners” from parallel universes. “I think King is writing one big book,” says longtime King chronicler Stephen J. Spignesi, who argues that “the entire body of King’s work exists in his [shared] universe.”

The net result of King’s creative labors is a universe that’s almost Tolkienian in its complexity, and a little like the worlds of Lovecraft or Robert E. Howard, but unique in the way its tapestry extends into so many settings and times. The deeper one’s awareness of the connections, the deeper one’s appreciation for King. “Everybody likes to be a part of that game that King is playing with the Constant Reader, where it’s not necessarily integral to the narrative he’s presenting to you, but he’s giving you a little bit of added frosting on that cake,” says Stanley Wiater, one of three writers who were among the first to map King’s grand plan in the 2001 guide The Stephen King Universe.

You can play, too. After consulting with Wiater and several other King chroniclers, I’ve come up with the following list of the works that are most central to King’s secondary universe. They’re far from the only linked entries in his oeuvre, but they’re the essential ones to seek out if you want to start spelunking the hidden depths of King’s celebrated body of work.

10. The Mist (1980)

The Mist takes place in Bridgton, Maine, where Roland and his companions venture in The Dark Tower series to search for Stephen King. Although Bridgton isn’t one of King’s most common haunts, Beahm, who thinks the novella may be the best entry into King’s voluminous library, says that “the sense of place that you get in The Mist is very typical of King.” Like a lot of King’s stories, including more recent releases Under the Dome and Sleeping Beauties, its setup (the unexplained arrival of a pervasive, monster-filled mist) forces ordinary people in an ordinary town to confront extraordinary circumstances that expose their good and bad sides. In other words, it’s an almost archetypal tale. And it takes on an added dimension in light of later writing, which makes clear—well, as clear as such concepts can be—that The Mist’s monsters were likely escapees through a thinny from todash space, helping blur the lines between King’s Dark Tower and ostensibly non–Dark Tower works.

9. The Eyes of the Dragon (1987)

A work of epic fantasy pitched toward younger readers, Eyes is an anomaly in King’s catalog, but it still forms a part of the tapestry as a quasi-prequel to The Dark Tower. The story is set in a region adjacent to where Roland is raised, Randall Flagg (see The Stand below) plays a prominent role, and Flagg’s pursuers, Thomas and Dennis, later merit a mention in The Dark Tower. Eyes also explains Flagg’s knack for avoiding notice and capture by making himself “dim”—not invisible, but “ghostly, transparent, unobtrusive.”

8. It (1986)

It is essential to the Derry mythos, and it also features some signposts that point to The Dark Tower. Based on his supernatural nature and his need to feed on children’s emotions, Pennywise is probably related in some sense to Dandelo, a creature from The Dark Tower, and the book also includes references to roses, Maturin the turtle (one of the guardians of the Beams that hold up the Tower), and other elements that appear in King’s fantasy cycle, like the nickname “Stuttering Bill” and an ageless adversary that calls itself “Legion.” Beyond those specific call-forwards, Pennywise’s presence in what appears to be a normal town, Furth says, reinforces the unifying sense in King’s interwoven work of “that underlying strangeness, that there is a world behind the worlds.”

7. Salem’s Lot (1975)

King’s second novel describes a town in Maine that reappears in two other short stories (and a Castle Rock episode) and is mentioned in many other books, but its biggest contribution to King’s secondary world is the character Father Callahan, who resurfaces as a major player in The Dark Tower V, Wolves of the Calla, and returns in books 6 and 7. In the latter book, an understandably confused Callahan comes across a copy of ’Salem’s Lot, which makes Calla a book by Stephen King about a character from an earlier book by Stephen King who actually encounters the earlier book in which he appears.

6. Hearts in Atlantis (1999)

Hearts combines two novellas and three short stories, all of which have characters in common and play out in roughly chronological order in 1960s America. Like Insomnia (see below), it marks the first appearance of a character who later reappears in The Dark Tower (the powerful Breaker Ted Brautigan), as well as another character (Bobby Garfield) who may be a twinner to The Dark Tower’s Jake. The longest piece of Hearts, “Low Men in Yellow Coats,” also introduces the “Low Men” or “Can-toi,” half-human servants of Roland’s ultimate enemy, Crimson King.

5. Insomnia (1994)

Insomnia is also set in Derry, and it’s rife with ties to It. Many of the same townspeople, geographic locations, and episodes from Derry’s history pop up again, and Mike Hanlon of It’s Losers’ Club even makes a cameo. But it’s also integral to The Dark Tower in that it introduces the Crimson King, an “It”-like entity that later becomes the Big Bad for the rest of Roland’s quest (and who, in another of Insomnia’s obvious allusions to It, says, “You may not know it, but shape-changing is a time-honored custom in Derry”). Another major character from Insomnia, Patrick Danville, also crosses over into the Dark Tower series and plays a pivotal role in the seventh book, published a decade after Insomnia. King has said that “Insomnia was the first place where I really understood [the links] consciously and I started to work all this stuff in there.”

4. The Talisman (1984)

The Talisman, a non–Dark Tower collaboration between King and Peter Straub, came out after The Gunslinger, but in retrospect, it’s one of the formative works that shaped what later installments of The Dark Tower cycle would look like. “That was when a lot of his ideas about Mid-World really coalesced,” Furth says. “He already had that world going … but it was almost like that collaboration really focused so much of what he was thinking already.” Much of The Talisman takes place in “The Territories,” a parallel reality that’s later mentioned in The Waste Lands (The Dark Tower Book 3) and Lisey’s Story. In establishing that setting, the story introduces “twinners” (identical individuals in parallel worlds) as well as “The White,” concepts that are central to later events in The Dark Tower. In addition, The Talisman’s protagonist, Jack Sawyer, makes a minor appearance in the 1987 novel The Tommyknockers, which unlike The Talisman takes place in Maine.

3. Black House (2001)

Black House, a second collaboration with Straub, also stars Jack Sawyer. Despite also not officially belonging to the Dark Tower narrative, this one explicitly refers to many Dark Tower characters, incorporates the Crimson King and, crucially, explains the concept of “Breakers,” powerful psychics whom the Crimson King later enlists to break the Beams that support the Dark Tower. Vincent considers Black House (along with Insomnia) a “testing ground” for Dark Tower plot points. But by labeling the Breakers, it also implicitly links The Dark Tower to some of King’s pre-Tower works, including Carrie, The Shining, The Dead Zone, and Firestarter, all of which featured characters with the same telepathic or telekinetic abilities—probably Breakers themselves, even if King didn’t use that term at that time.

2. The Stand (1978)

The Stand, King’s epic, postapocalyptic fifth novel, solidifies what Furth calls “that dynamic of the good lawman versus this chaotic energy,” the Lord of the Flies–inspired tension that serves as the foundation for so much of King’s work. It also introduces Randall Flagg, King’s most memorable and frequently recurring villain, who represents chaos and evil in all of its forms and appears or is referenced in at least a dozen stories. Flagg, who goes by many names both in The Stand and elsewhere (one of which is borrowed from Lovecraft), is also the “man in black” mentioned in The Gunslinger’s famous first sentence, who torments Roland throughout the Dark Tower series. In Wizard and Glass, Roland and his fellow travelers visit a Topeka that appears to be part of the same level of the Tower on which The Stand is set.

1. The Dark Tower (1982-2012)

“I am coming to understand that Roland’s world (or worlds) actually contains all the others of my making,” King wrote in the afterword to the fourth installment of the Dark Tower series, 1997’s Wizard and Glass. Or as Vincent puts it, “The Dark Tower is the be-all and end-all of the shared universe.”

King’s crowning achievement in The Dark Tower isn’t just that he managed to cram references to almost every major work of his 45-year career into one series. It’s that those references reveal the ultimate purpose of building back doors between books in the first place. As linguist Lizzie Stewart-Shaw, who adapted her master’s thesis into an essay for Pennywise Dreadful about intertextuality in The Dark Tower, observes via email, “King’s inclusion of so many intertextual references to his own works actually thematically strengthens the premise of the Dark Tower series, which is that all possible worlds intersect at the Dark Tower itself.” Once they dig The Dark Tower, Constant Readers start seeing the source code behind decades of King’s work.

As Furth explains, those epiphanies are what make King’s interconnected universe so satisfying. In the Kingverse, “things make a kind of sense. There’s meaning, there are echoes from one world to another. What happens in our world will be related to something bigger occurring on a parallel level of reality.” And when one’s own world is imperfect, “there are other worlds than these” can become a comforting thought.