September 17 is designated as Constitution Day and Citizenship Day to commemorate the signing of the U.S. Constitution in Philadelphia on September 17, 1787. 

Source: https://www.archives.gov/news/topics/constitution-day#:~:text=September….

Preamble

We the People of the United States, in Order to form a more perfect Union, establish Justice, insure domestic Tranquility, provide for the common defense, promote the general Welfare, and secure the Blessings of Liberty to ourselves and our Posterity, do ordain and establish this Constitution for the United States of America.

Source: https://www.senate.gov/about/origins-foundations/senate-and-constitutio…