The title of Byron's "The Prisoner of Chillon" is, like so many titles, deceptively simple. At first glance, the title seems just to be a label that tells us what the poem is going to be about. But when we start asking questions, things start getting a bit messier.
The title refers us to a real place – Chillon Castle, which is on the shores of Lake Geneva and is still there to this day. (Check out the pictures in the "Best of the Web" section, and plan on dropping by on your next trip to Switzerland!) Besides referring us to the real-life castle dungeon where the poem takes place, the title tells us whom it's going to be about: a "prisoner."
OK, but what prisoner? Doesn't the guy have a name? Well, Byron's "Sonnet on Chillon" (get the text here), which is often published alongside "The Prisoner of Chillon" as a kind of introduction, mentions the historical inspiration for the poem by name. The real-life "Prisoner of Chillon" was named François Bonnivard and lived in the 1500s. His story was picked up by later generations and he was made into a kind of popular folk hero.
But Byron's poem isn't purely history – he takes a lot of liberties with historical fact, and he alerts us to that with the subtitle of the poem: "A Fable." What's a fable? It's a simple, fictional story, usually with a moral. Maybe Byron warns us that his poem is a "fable" so that we'll be on the lookout for a universal moral, rather than the particular story of one individual. Leaving the "Prisoner of Chillon" unnamed suggests that we're supposed to think of him as representative for all the people who have suffered from unjust imprisonment or tyranny of any kind. Calling the poem "a Fable" just reinforces the idea of universality.