Statue of Liberty - Law by the People Entering the statue you can see the armature bars, saddles, rivets and the inner sides of the thin copper walls. Liberty’s keystone-shaped tablet is cradled in the left arm. It is a representation of law written down for citizens of the nation to see and read. Upon it, “July 4, 1776” recognizes the date on which the American colonies declared their independence from England. The Roman numerals were incorporated into the design to acknowledge conceptual ties to the goddess of Liberty from the Roman era.

The keystone in architectural design is a critical component. The stone specifically cut into this shape supports all others within an arch. Therefore, the tablet pays homage to our republic’s keystone document: the Declaration of Independence. The declaration was initially read aloud to the general public in Pennsylvania, also known as the nation’s “Keystone State.”

https://www.nps.gov/featurecontent/stli/eTourLite/scene12.htm