PHILADELPHIA (CBS)– A priceless piece of American history is sitting in a records office in England and the woman who discovered it was in Philadelphia to talk about its importance.

“We came across the catalogue entry and the catalogue entry said manuscript entry on parchment,” said Emily Sneff.

Sneff is originally from Philadelphia, but currently works as a research manager at Harvard University. She was cataloging various copies of the Declaration of Independence across the globe when she discovered the rare handwritten copy in southern England.

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“We had to request an image so it wasn’t until we saw an image and then started kind of zooming in on the image and found things that made it really unique and really interesting,” said Sneff.

“This is the place where we think this document was read as part of the Constitutional Convention,” said Danielle Allen, with Harvard University

Sneff and Allen believe this new discovery was written around 1786 and read aloud by James Willson—a Pennsylvanian who signed both the Declaration and Constitution.

The document is the same size as the original, but what makes this unique is that the signatures are written by one person and they are not in a particular order.

“John Hancock is listed fourth instead of first and we believe it was intentional these names were listed in a different order,” Sneff said.