September 17, 1787
As an institution, the Senate can claim several starting dates. In 1987, senators and representatives traveled to Philadelphia to commemorate one of them—July 16. On July 16, 1787, the Constitution's framers arrived at the so-called "Great Compromise," which provided that states would be represented equally in the Senate and in proportion to their populations in the House. Without that compromise, there would likely have been no Constitution, no Senate, and no United States as we know it today.
A second major beginning date is September 30. On that day in 1788, the Pennsylvania legislature elected the nation's first two U.S. senators—Robert Morris and William Maclay. The election of Maclay proved particularly important because he was the only member of the First Senate to keep a diary at a time when all Senate sessions were held behind closed doors.
April 6 ranks near the top of any list of Senate anniversaries. On April 6, 1789, the Senate mustered its first quorum—five weeks late. The Senate's first order of business was to meet jointly with the House to count the electoral ballots that formally gave George Washington his presidential victory.
Finally, there is September 17. On September 17, 1787, thirty-nine of the convention's fifty-five delegates signed the United States Constitution at Independence Hall in Philadelphia. Of those thirty-nine, sixteen went on to become U.S. senators.
In selecting an appropriate visual symbol of the Senate in its founding period, one might consider an anchor, a fence, or a saucer. Writing to Thomas Jefferson, who had been out of the country during the Constitutional Convention, James Madison explained that the Constitution's framers considered the Senate to be the great "anchor" of the government. To the framers themselves, Madison explained that the Senate would be a "necessary fence" against the "fickleness and passion" that tended to influence the attitudes of the general public and members of the House of Representatives. George Washington is said to have told Jefferson that the framers had created the Senate to "cool" House legislation just as a saucer was used to cool hot tea.
Perhaps Pennsylvania's James Wilson, a convention delegate, should have the last word on this anniversary. In the fall of 1787 he told the citizens of Philadelphia that he was amazed that the Senate had been created at all. "For my part, my admiration can only be equaled by my astonishment in beholding so perfect a system formed from such heterogeneous materials."
Baker, Richard A. The Senate of the United States: A Bicentennial History. Malabar, FL.: Krieger Publishers, 1988.