One day after a snowstorm shut down D.C., Congress is back in session today. Its hearings might not make much news, but March 4 is actually an astonishing anniversary. It was 225 years ago that the Constitution officially came into effect, when members of Congress were sworn in for the first time in New York City.

They didn’t have what today might be called a quorum, though. Only nine (out of an elected 22) senators and 13 (out of an elected 59) representatives were on hand that day. Furthermore, only 11 of the 13 states had ratified the Constitution at that time.

See also: The Formation of the Constitution

The sparsely attended session marked the beginning of a noble, and uniquely successful, experiment. The U.S. has the oldest national Constitution in continuous use. It successfully set up a republican democracy to govern a continental nation. In the centuries since, the Constitution has endured through economic booms and busts, and survived wars at home and abroad.

The Constitution’s very staying power is noteworthy. Since the end of World War II, at least 188 countries have drafted at least 729 versions of constitutions, while we’ve made only minor changes to ours through a constitutionally-provided amendment process. Our Constitution is unique in its simplicity, and uniquely effective.

Ironically, one of the first orders of business under the Constitution was to begin changing the Constitution. A number of states had insisted that a Bill of Rights should be added, and the members of Congress (led by Rep. James Madison) got to work writing that.

See also: Securing Liberty: The Purpose and Importance of the Bill of Rights

They eventually drafted 12 amendments and, in September of 1789, sent them to the states for ratification. Ten of those became the Bill of Rights. An eleventh, saying that congressional pay couldn’t be changed until after an election had intervened, waited for more than 200 years. It didn’t become the 27th Amendment until it was ratified in 1992.

George Washington, the first president, wasn’t on hand in March of 1789. It took longer than expected to count the Electoral Votes, so his swearing-in didn’t happen until late April.