What is happening in the first four lines of the story "The Pit and the Pendulum"? Describe the dramatic tension that this opening creates.

This question refers to the four-line Latin epigraph that comes at the beginning of the story. The quatrain speaks of the Jacobins, a party of men who ruled France after the French Revolution. Although the Jacobins were moderates at first, they soon became despotic and initiated the Reign of Terror in France, where they killed their enemies wantonly with the guillotine. The quatrain was written in hindsight about the Jacobins, after they were no longer...

This question refers to the four-line Latin epigraph that comes at the beginning of the story. The quatrain speaks of the Jacobins, a party of men who ruled France after the French Revolution. Although the Jacobins were moderates at first, they soon became despotic and initiated the Reign of Terror in France, where they killed their enemies wantonly with the guillotine. The quatrain was written in hindsight about the Jacobins, after they were no longer in power, and was purportedly engraved at the gates of a marketplace that was built on the site of the Jacobin Club House in Paris.

The first two lines of the quatrain translate as:

Here the wicked mob, unappeased,
long cherished a hatred of innocent blood. 

The actions these lines describe, and knowing they refer to the Reign of Terror, create tension in the story by setting up an expectation of a tale of hatred and bloodshed by forces that are as unstoppable as a "wicked mob." They also imply that the person or persons at the receiving end of the mob action are innocent. So from the beginning of the story, readers expect a horrific and unjust scene of violence by unscrupulous perpetrators on an innocent party. This creates tension.

The other two lines of the quatrain look beyond the end of the reign of terror: 

Now that the fatherland is saved, and the cave of death demolished;
Where grim death has been, life and health appear.

Even though this foreshadows a happy ending for the story ("life and health appear"), the reader doesn't know whether that happy ending comes in time to benefit the one or ones who are unjustly attacked. This creates additional tension: Will the salvation come in time? Obviously for many of those killed during the Reign of Terror, it didn't. 

Understanding the meaning of the quatrain and its allusion to the Jacobin Reign of Terror prepares the reader for a story of undeserved violence with an ambiguous hint at a happy ending.