At 8:00 p.m. on September 24, 1849, Edgar Poe presented his last lecture on "The Poetic Principle." Held at the Exchange Hotel in Richmond, Poe's lecture discussed his poetic theory, particularly that a poem should be written merely for the sake of being a poem, not as instruction. Poetry is art, he implies, and therefore should focus on pure beauty and aesthetics. He also says that a poem should be short, able to be read in a single sitting. He gave specific examples of poets he thought were good, and others he thought were bad.
Poe had given lectures on the topic before, including one in Richmond. In fact, the local newspaper that day, Daily Republican, noted, "Although it is a repetition, we are sure that few, if any, who attended his first lecture, would be unwilling to hear it over again, and those who were not present on that occasion, will deprive themselves of a delightful entertainment by failing to attend to-night." One of the audience members was Sarah Elmira Royster Shelton, who supposedly had a prime seat in the front row. 57 years later, the (usually unreliable source) Susan Archer Talley wrote that Rosalie Poe was there too.
We don't know for sure what was said in the original lectures. His first versions of it were lost or stolen and had to be rewritten. The manuscript from his September lecture in Richmond, however, apparently survived and was found in Poe's trunk after his death. According to the Edgar Allan Poe Society of Baltimore, poet/editor Bayard Taylor wanted to sell this manuscript to George Graham for the benefit of Maria Clemm. Instead, it was purchased by John Sartain, who published it in his Union Magazine in October 1850. Taylor, working on behalf of Rufus Griswold, likely never turned the money over to Mrs. Clemm.
From that published version of the lecture, we see that Poe praises William Cullen Bryant ("The intense melancholy which seems to well up, perforce, to the surface of all the poet's cheerful sayings about his grave, we find thrilling us to the soul — while there is the truest poetic elevation in the thrill. The impression left is one of a pleasurable sadness.") as well as Edward Coote Pinkney, Lord Byron, and Lord Tennyson.
It was Poe's last public appearance before he vanished.