Epigraphs are like little appetizers to the great entrée of a story. They illuminate important aspects of the story, and they get us headed in the right direction.
Impia tortorum longas hic turba furors
Sanguinis innocui, non satiata, aluit.
Sospite nunc patria, fracto nunc funeris antro,
Mors ubi dira fuit vita salusque patent.
[Quatrain composed for the gates of a market to be erected upon the site of the Jacobin Club House at Paris.]
Translation: "Here an unholy mob of torturers with an insatiable thirst for innocent blood, once fed their long frenzy. Now our homeland is safe, the funereal cave destroyed, and life and health appear where dreadful death once was.'' (Source.)
What's Up With the Epigraph? :
Time for a history lesson, folks: though Poe puts his protagonist in the hands of the Spanish Inquisition, his epigraph refers to another "unholy mob of torturers" – in this case, the members of the Jacobin Club. Unfortunately, this is not your typical club with bake sales, cool t-shirts, and a nifty yearbook page. For a little history snack and the dirt on the Jacobin Club, check out the Britannica page. And then, read on.
After the French monarchy fell at the beginning of the 1790s, members of the Jacobin Club assumed power in the new National Convention that governed France (goodbye kings and queens). Though their politics were moderate at first, they became more and more radical as time went on. By 1793, the Jacobins pretty much took control of the government, and with their newfound power, they began to remove their enemies from the Convention. In the last months of their rule, which came to an end in the summer of 1794, the Jacobins began executing their enemies willy-nilly – often using the guillotine – during what would become known as "The Reign of Terror."
Okay, so now you know why the Jacobins deserve that whole "unholy mob of torturers" nickname. You must then be wondering, why didn't Poe just write about them? Well, as awful as the Reign of Terror was, it just doesn't bring to mind those same sinister images as the Spanish Inquisition. It's this eerie reputation that Poe wants to exploit and which allows him to basically invent whatever crazy tortures he wants (as opposed to just sticking with a guillotine). By including the epigraph, he can refer to these more recent events while still letting his imagination run wild.