Signing of the U.S Constitution at Philadelphia Convention (public domain image on Wikipedia).
Official State Nickname of Pennsylvania
Pennsylvania's nickname is "The Keystone State" because it was the middle colony of the original thirteen colonies, and because Pennsylvania has held a key position in the economic, social, and political development of the United States. All State Nicknames
Three of our most treasured documents are associated with Pennsylvania: the Declaration of independence and the United States Constitution (both executed in Philadelphia), and Lincoln's Gettysburg Address.
Pennsylvania's state song mentions the state nickname in the second verse: "Birthplace of a mighty nation, Keystone of the land." A keystone is also featured on the U.S. Mint's Pennsylvania quarter.
What is a Keystone?
The word keystone is from architecture, it describes the central wedge-shaped stone in an arch which holds all the other stones in place.
