About the time of Bacon's Rebellion, in Virginia, strenuous efforts were made to protect the frontier line which ran along the falls of the river, against the attacks of Indians. This "fall line," as the geographers call it, marking the head of navigation, and thus the boundary of the maritime or lowland South, runs from the site of Washington, through Richmond, and on to Raleigh, North Carolina, and Columbia, South Carolina. Virginia having earliest advanced thus far to the interior, found it necessary in the closing years of the seventeenth century to draw a military frontier along this line. As early as 1675 a statute was enacted,[84:1] providing that paid troops of five hundred men should be drawn from the midland and most secure parts of the country and placed on the "heads of the rivers" and other places fronting upon the Indians. What was meant by the "heads of the rivers," is shown by the fact that several of these forts were located either at the falls of the rivers or just above tidewater, as follows: one on the lower Potomac in Stafford County; one near the falls of the Rappahannock; one on the Mattapony; one on the Pamunky; one at the falls of the James (near the site of Richmond); one near the falls of the Appomattox, and others on the Blackwater, the Nansemond, and the Accomac peninsula, all in the eastern part of Virginia. Again, in 1679, similar provision was made,[84:2] and an especially interesting act was passed, making _quasi_ manorial grants to Major Lawrence Smith and Captain William Byrd, "to seate certain lands at the head [falls] of Rappahannock and James river" respectively. This scheme failed for lack of approval by the authorities in England.[84:3] But Byrd at the falls of the James near the present site of Richmond, Robert Beverley on the Rappahannock, and other frontier commanders on the York and Potomac, continued to undertake colonial defense. The system of mounted rangers was established in 1691, by which a lieutenant, eleven soldiers, and two Indians at the "heads" or falls of each great river were to scout for enemy,[85:1] and the Indian boundary line was strictly defined.