No definite effort was made at the time of the recession of Alexandria County to Virginia to draw a boundary line between the County and the remaining portion of the District of Columbia. As noted above, the various acts bringing about the recession referred only to "the territory heretofore ceded by the Commonwealth of Virginia." The actual boundary was of small moment at the time. Toward the end of the 19th Century, however, the United States Government acquired lands on the Virginia shore of the Potomac largely through the purchase of the Arlington estate. As the 20th Century progressed, roads (notably the Mount Vernon Boulevard and later the George Washington Memorial Parkway) were constructed, bridges and bridge approaches built and, eventually, the Federal Government undertook to construct the National Airport at Gravelly Point below Alexander's Island. A suit[59] over government activity in making a land fill raised questions as to the exact location of the boundary--and indeed as to whether Alexander's Island really was an island or was a peninsula. This case, decided by the U.S. Supreme Court on May 4, 1931, set the boundary line between the District of Columbia and Virginia at the high water mark of the Potomac on the Virginia shore as it existed in 1791. [59] _Washington Airport_ vs. _Smoot Sand and Gravel Corp_., 283 U.S. 348. Cf. also, _Marine Railroad and Coal Co_. v. _U.S._, 257 U.S. 47. But where had that high water mark been? There had been no survey at the time; the shore line had never been marked; and even had it been, the passage of time had made many changes in the river front.[60] A Commission was established[61] to deal with this question. The instructions to this Commission were to take into consideration the decisions of the Supreme Court of the United States, the findings and report of the Maryland-Virginia Commission of 1877[62] and the Maryland-Virginia compact of 1785.[63] [60] This indefinite boundary line "lies in many places some distance from the Potomac River." _Report No. 895_, H.R., 78th Congress, 1st Session. [61] 48 U.S. Stat. 453; Virginia Acts of Assembly, 1932, p. 485.