Think Shakespeare invented the idea of star-crossed lovers? Not so much. Before Romeo and Juliet, even before Lancelot and Guinevere, Tristan and Isolde (or, in Béroul's version, Yseut), ruled ye olde roost as the star-crossed lovers who started it all. Beginning in the early 12th century, this Celtic folk tale of ill-fated love between a Cornish knight and his king's wife was insanely popular, first in northern France and then all over Europe. No big deal.

Oh, and it basically changed the way we think about love.

See, the legend stayed popular way after Béroul wrote his poem (The Romance of Tristan). There are a ton of retellings out there—in prose, verse, and, later, opera and film—right up until the present day. The love affair of Guinevere and Lancelot is probably inspired by this story, as are elements of Shakespeare's tale of Romeo and Juliet. Now there are a lot of love stories out there. But you can get your sex-and-violence fix in pretty much any flavor you like these days. So what is it about this legend that made it so popular?

For one thing, it's about a really juicy love triangle. Yseut is the wife of Tristan's uncle and lord (awkward!), so when the two lovers decide to chuck it all and have an affair, it's like they're breaking every single rule in the book. Seriously. Way back in medieval times, the most important love in a knight's life was the love he owed his lord, followed by love for his fellow knights. As we would put it today: bros before… not bros. Are we right? But in this story we have a knight who is like, "Sorry, dudes, I'm in love. I just can't help myself!"

So here we have a story that wants to explore the conflict between different kinds of love relationships: the love between a lord and his vassal vs. the love between a woman and a man, to name just one. The story of Tristan and Yseut got popular at a time when the definition of marriage was changing from a contractual relationship between two families into a love relationship between two individuals. Romantic love (sigh) was becoming way more important than it ever had been in the past. This story asks the question: When your romantic love is for the wife of your lord, which love should win out?

Then it goes one step further and asks, What is love, anyway? Tristan and Yseut get kind of a free pass in this story because they accidentally drink a love potion on their way to Cornwall. Now, if you fall in love because you accidentally drink a love potion, it's not really your fault, right? You can't control it. It just happened to you. It's like fate. You can't ignore it. If it's your fate, you have to go through with it, right? So this story raises the possibility that even if your love causes harm or destruction, you're not completely to blame for it. The love potion shows the all-consuming power of love. Maybe all love makes you just as powerless to resist your fate. You can thank Tristan and Yseut for that lesson.

P.S. We should also mention that most of the plot in this story revolves around the lovers' attempts to snog behind the king's back. Read on!

(Spoiler alert!)

Have you ever had a crush on someone you just couldn't be with? Your heart beats a little bit faster when they approach. Your palms sweat. Maybe you blush. You're convinced that the thing that would make you happiest in the world is just to love that person and have them love you back. Maybe people tell you to "just get over it." But as anybody who's had a really intense crush knows: You. Just. Can't. You're powerless to resist what your heart is telling you. The heart wants what it wants.

Tristan and Yseut are powerless to resist their feelings, too, in this case because of a magical potion that causes them to fall hopelessly, helplessly in love with one another. There's just one problem: Yseut is the wife of another man. And not just any man: Tristan's lord and uncle.

Now this is bad. Real bad. In medieval Cornwall, adultery with the queen is not just wrong; it's also a crime, punishable by death. That's right: they can kill you for this stuff. That doesn't stop Tristan and Yseut, though. And just like when you're crushing hard and feeling totally, totally emo about it, Tristan and Yseut are tormented by their love, too. It makes them do things they wouldn't normally do. Tristan betrays his lord and uncle. Yseut gives up the life of a queen to live like a beggar in the forest with Tristan. When they're separated, Tristan feels like he's going insane. They didn't do things halfway back then.

Unfortunately, the story doesn't end well. There are just too many obstacles to their love like, oh, the people they're married to. Even though in the end they are unable to be together, Tristan and Yseut's star-crossed love inspires countless imitators, like Lancelot and Guinevere and Romeo and Juliet. The message seems to be that love itself—even if it's forbidden, even if it can never be fulfilled—is worthwhile for its own sake. So go ahead: indulge that crush, knowing that it may never go anywhere. But take a little time to remember Tristan and Yseut, and read this Shmoop guide while you do.