"... from and immediately after the first day of December now next ensuing, the said county of Prince William be divided into two counties: That is to say, all that part thereof, lying on the south side of Occoquan, and Bull Run; and from the head of the main branch of Bull Run, by a straight course to the Thoroughfare of the Blue Ridge of mountains, known by the name of Ashby's Gap or Bent, shall be one distinct county, and retain the name of Prince William County: And be one distinct parish, and retain the name of Hamilton parish. And all that other part thereof, consisting of the parish of Truro, shall be one other distinct county, and called and known by the name of Fairfax county...."[19] [19] Acts of Assembly, May 1742, Chapter XXVII. Hening, Vol. v, p. 207. Thus from December 1742 until the District of Columbia was formally organized by Act of Congress (February 27, 1801) what is now Arlington was part of Fairfax County. _1789-1847_ Maryland and Virginia had agreed to meet in 1785 to discuss the controversy over the navigation of the Potomac and their joint boundary. The Commissioners who took part in this meeting did more than draw up a compact subsequently ratified by their respective States. From this meeting eventually came the call for the convention which resulted in the Constitution of the United States and the decision to set aside a tract of land ten miles square for the seat of the Federal Government. The Maryland-Virginia compact on the Potomac was signed on March 28, 1785, and confirmed by the General Assembly of Virginia in 1786.[20] Although it was designed primarily to settle navigation and fishing rights, its seventh section provided: "The citizens of each State, respectively, shall have full property rights in the shores of Patowmack river adjoining their land...." This has been interpreted to mean property rights to low water mark. The dispute over this point became of significance in the 20th Century with the construction of the National Airport and the Pentagon Building. [20] Acts of Assembly, 1785, Chapter XVII. Hening, Vol. xii, pp. 50-55. Cf. also _Code of Virginia, 1950_, Title 7.1, Section 7, and Conway, _The Compacts of Virginia_, p. 5. The Potomac River Fisheries Compact of 1958 (Acts of Assembly, 1962, Chapter 406; _Code of Virginia 1950_, Title 28.1, Sec. 203) did not affect Arlington. Article I, Section 8, of the Constitution of the United States gives the Congress power to accept a territory not exceeding ten miles square to be set aside as the seat of the Federal Government. The story of the compromise which led to the selection of a site on the Potomac is told in all the history books.[21] These, however, rarely give the details of how the exact area which became the District of Columbia came to be chosen.