For people who are Shakespeare nuts, 2016 was pretty exciting. Not only was it the 400th anniversary of his death in 1616, but in honor of his death, 18 copies of Shakespeare First Folios—the first collected published edition of his work—were exhibited at libraries and universities in each of the 50 states.

Then, to make things even more exciting, a previously unknown copy of his First Folios was found in a Scottish manor, two years after one had been found at a library in France. It was like the way another copy of the Magna Carta was found during the celebration of its 700th anniversary.

“First folios are tracked like rare black rhinoceroses, right down to their disappearances,” writes Jennifer Schuessler in the New York Times. “One is known to have burned in the Great Chicago Fire of 1871; another went down with the S.S. Arctic off Newfoundland in 1854. New ones come to light every decade or so.”

That there’s even a First Folio at all is unusual, writes Sean Adams in PennLive. Back in the day, plays weren’t published for people to be able to read later. “It was very common for poems to be printed and read as literature, but not plays,” he quotes Joshua Cohen, Instruction and Outreach Librarian at Elizabethtown College, as saying. “Plays were considered popular entertainment. It would be like people sitting down and reading TV scripts or something like that. It’s just not something people do.”

But seven years after Shakespeare’s death, two members of his company collected 36 of the plays into a single book, and published 750 copies of it, Adams writes. 18 of the plays—including some of his now best-known ones, such as Macbeth and The Tempest—had never been printed before the book, which would have sold for $250, writes Dan Whisenhunt for Decaturish.com. Copies of it have sold today for as much as $6.1 million.

“Theater historians estimate that about one-sixth of all plays performed in the early modern period (up until 1642 when the theaters were closed) are extant,” writes Micah Mattix in the Weekly Standard. “Another sixth are known by their titles only.” Publishing the First Folio meant that 18 plays wouldn’t have joined them. “Those plays would join the ranks of Cardenio, a play that scholars know was performed by Shakespeare’s acting troupe, but no copies exist today,” Adams writes. (And while there are Second, Third, and Fourth folios, they are thought to contain works not necessarily written by Shakespeare, Whisenhunt adds.)

Even with the plays that had previously been printed, the lines we know of today typically come from the First Folio rather than an older version. For example, how many of us have heard the original line from Hamlet: “To be, or not to be, ay, there’s the point”? (Incidentally, all the exhibited First Folios were opened to that page.)

Of the 750 copies, there are now 233 known to exist today—a pretty remarkable number for a 400-year-old book, Adams writes. The Folger Shakespeare Library, which arranged the tour, owns 82 of them, he adds.

In addition, two laptops containing PDFs of the Folio let attendees zoom in on pages or find their favorite Shakespeare passages. Other digitized First Folios are also available online in multiple formats, as are associated Shakespeare materials and material from the Globe Theater.

The copies of the First Folio aren’t all alike. As with the Declaration of Independence, there are tiny differences between each copy, Whisenhunt writes. “First Folio scholars can give you a granular detail on most of the existing copies, who the typesetters where, where the typos and watermarks are, the individual history of who possessed the books and when,” he writes. “In some manuscripts, even shadows of the editing process are present, like named characters that don’t appear in the final draft, which are referred to as ‘ghost characters.’”

For example, the French discovery contained marginalia, or annotations that help describe how the plays were performed, Schuessler writes. “In one scene in Henry IV, the word ‘hostess’ is changed to ‘host’ and ‘wench’ to ‘fellow’—possibly reflecting an early performance where a female character was turned into a male.”

If you aren’t into the theatre or literature, chances are that you still quote Shakespeare every day, even if you don’t know it. “Without Shakespeare, you wouldn’t be able to ‘break the ice’ during an awkward silence, or say ‘good riddance’ when the guest causing the awkward silence decided to leave,” Whisenhunt writes. “Reporters wouldn’t be able to go on a ‘wild goose chase’ to track down a lead that doesn’t pan out, or ‘play fast and loose’ with the facts. Alabama winning football games would not be a ‘foregone conclusion.’ Love would not be blind and no one would be a ‘laughing stock.’ And when you love, you could not say, I ‘wear my heart upon my sleeve’ and it wouldn’t be a ‘heart of gold.’ You couldn’t say your child will ‘eat me out of house and home.’ Articles, speeches and essays would be longer without the sage advice that ‘brevity is the soul of wit.’ And when your time on this earth had ended, you would not be ‘dead as a door nail.’”

Even the simple “knock knock” joke would be a casualty: “Knock knock jokes come from Macbeth,” Whisenhunt explains.