Imagine a time before computers and the safety net of spellcheck and auto-correct. Imagine you are about to write by hand (or “engross”) the document that will set out the fundamentals of governing a new nation. And you have less than 48 hours to do it.

The Constitution (plus its “fifth page” were written by one man. Someone set quill to parchment and wrote over 25,000 letters (over 4,000 words) on four large pieces of parchment. Over a million visitors come to see his handiwork every day at the National Archives.

But for many years, his identity was unknown. Because most of the papers of the Constitutional Convention were ordered to be destroyed, the only paper trail was a single receipt for a payment of $30. No name was recorded.

In 1937, he was finally identified by historian John Clement Fitzpatrick, who wrote an article for the 150th anniversary of the Constitution. At last, the world knew the name of the engrosser: Jacob Shallus.

Shallus, the son of German immigrants, lived in Philadelphia with his growing family. He was also a Revolutionary War veteran. He volunteered and served as a battalion quartermaster under Col. John Philip de Haas. (In 1777, Shallus wrote to John Hancock from wartime headquarters in Lancaster, PA, about a beef supplier demanding payment. This is the earliest example we have of his handwriting.)

Jacob Shallus was working as assistant clerk for the Pennsylvania General Assembly. He was elected to the position in the fall of 1787, and he was working upstairs in the West Wing of the State House at Philadelphia while the Federal Convention concluded a hot summer of work in the larger East Chamber below. On September 15 around 6 p.m., the delegates cried “aye” when James Madison moved that the most recent revised draft adopted. The session adjourned until Monday, when the Constitution would be signed by the delegates.

They needed a clerk who could be trusted, who was competent, and who was close by. Jacob Shallus was upstairs.

Shallus had from Saturday evening to Sunday night to take the drafts, notes, and revisions and create an accurate transcription. In his book The Man Behind the Quill, Arthur Plotnik estimates that Shallus had about 40 hours between receiving the drafts and handing back the engrossed parchment, but that after accounting for eating and sleeping, the number of working hours was more likely 35. Plotnik estimates the “slowest possible pace” to be about 160 words an hour. Shallus had to write over 4,000 words.

He completed his task in an elegant hand, on time.

But even an experienced clerk like Shallus made mistakes. In the days before “delete,” there was only thing he could do. He added in an “errata” at the very end of the document, just above the signatures. This note listed the errors and corrections, all fairly minor but needing notation. But even these corrections had errors! Shallus incorrectly identified the lines where one of the correction was.

Plotnik notes that these minor errors do not take away from a successful job. “The script was every bit as dignified as the prose and as bold as the concepts of the momentous document,” he writes.

You can admire Shallus’s work in the Rotunda at the National Archives, where the Constitution is on permanent display. And from September 14 to 19, you can see the transmittal page (also known as the “fifth page” of the Constitution), also engrossed by Shallus.

(And if you are on Twitter, @Archivespres will be channeling Jacob Shallus! Follow his thoughts as he completes his monumental task.)