In 1723, a teenage Benjamin Franklin, newly arrived in Philadelphia, printed his first work in the city, an elegy on the recent death of a poet and pressman.
The broadside surfaced in the 1820s, then disappeared from public view for nearly 200 years.
But now, the only known copy of the printing is on display and available to the public and scholars.
Penn recently acquired the copy, the last formerly missing piece of Franklin's printing, according the library. A book dealer found the printing in a scrapbook, which is also on display.
The library noted that Franklin's impressive presswork on the broadside likely earned him a job as a pressman and kept him in Philadelphia, forever altering his – and the city's – path.
Franklin was born in Boston but ran away to Philadelphia at age 17.
In his autobiography, Franklin wrote that it was Rose's death that prompted him to set out for Philadelphia. Another printer told the young Franklin that he did not have enough work to offer the teenager, but: "My son at Philadelphia has lately lost his principal hand, Aquilla Rose, by death; if you go thither, I believe he may employ you."
In Philadelphia and searching for work, Franklin was introduced to another printer, Samuel Keimer, who was composing the elegy to Rose.
Decades later, Franklin recounted the episode in his autobiography: "Keimer's printing-house, I found, consisted of an old shatter'd press, and one small, worn-out font of English, which he was then using himself, composing an Elegy on Aquilla Rose ... So there being no copy, but one pair of cases, and the Elegy likely to require all the letter, no one could help him. I endeavour'd to put his press ... into order fit to be work'd with; and, promising to come and print off his Elegy as soon as he should have got it ready ... A few days after, Keimer sent for me to print off the Elegy. And now he had got another pair of cases, and a pamphlet to reprint, on which he set me to work."