Philadelphia hosted the 1787 Constitutional Convention commemorated in the history of the United States Semiquincentennial.
Delegates met at the Pennsylvania State House, now called Independence Hall, from May 25 to September 17, 1787. Although the convention was officially called to revise the Articles of Confederation, its delegates ultimately drafted an entirely new Constitution.
Philadelphia was already a major political center and had hosted the Second Continental Congress and the signing of the Declaration of Independence. The city therefore had strong practical and symbolic importance during the founding era.
A common mix-up is confusing the Constitutional Convention with the First Continental Congress, which also met in Philadelphia but took place in 1774. The convention’s work produced the framework of the federal government celebrated in later national anniversaries.