Historical Context in The Cask of Amontillado

"The Cask of Amontillado" incorporates Carnival and the Freemasons, both of which would have been widely known to Poe’s audience, in order to advance Montresor’s plans for revenge.
The Freemasons are an international, fraternal society that was established to support its members’ moral and spiritual values. The group has been historically composed of extremely wealthy men and engaged in secret rituals. During Poe’s time, the group was considered sacrilegious.
Carnival is the massive public celebration before Catholic Lent that consists of parades, circuses, elaborate costumes, and excessive consumption of alcohol, meats, and other indulgences restricted by Lent. People often wear masks to conceal their identities and create a greater sense of social unity.

Both of these historical points allow Poe to tell his story. First, Carnival creates a chaotic setting where no one would notice Montresor leading Fortunato into the catacombs. Second, in making Fortunato a Freemason, Poe implies that Fortunato is an unlikable character.

The Cask of Amontillado 3
"you are happy, as once I was..."   (The Cask of Amontillado)

Poe, like his character Montresor, knew what it was to fall on hard times. After a falling out with his wealthy foster father, Poe lost his high social status, and suffered from chronic financial troubles--as well as alcoholism--for the rest of his life. A quarrel Poe had with two other poets may also have inspired his tale of revenge.

"the brotherhood..."   (The Cask of Amontillado)

Poe alludes here to the Masons, a fraternal organization which was widely considered sacrilegious during his time. By making Fortunado a Mason, Poe taps into the then-widespread sentiment against the group, as well as further illustrates Fortunado’s sense of superiority to Montresor.

"the carnival season..."   (The Cask of Amontillado)

In Catholic countries such as Italy and France, this is the period just before Lent when everyone celebrates to excess. Part of the celebration is to wear costumes that hide one's identity--a perfect time for Montresor to go unnoticed. The carnival season identifies the setting as Venice, whose carnival is world-famous and still attracts hordes of tourists.