These Virginian aristocrats got their name from an area. The Tidewater (also called Coastal Plain) is a region in east Virginia, comprising a near sea level alluvial plain subject to tides. It lies between Chesapeake Bay's western shore and the Fall Line. This line delineates the abutment of the soft material of the coastal plain against the rocks of the Appalachians. Like filling in the dots, a fall line also connects the waterfalls on rivers where each stream drops from the upland to the lowland as well as the navigability limit of each river. Hence, its name. The Tidewater is traversed by the James, Potomac, Rappahannock and York rivers, and their tidal estuaries. Jamestown was the original and most important Tidewater settlement. After many vicissitudes, its leaders found a viable economy in the cultivation of tobacco. When the frontier moved west off the Tidewater in the mid-1600s, English gentry took over. These tobacco plantation owners used their capital to shift from importing indentured servants to importing slaves as their primary means of production. As a result, they became quite wealthy. By 1700, a class of approximately five percent of the population, the "First Families of Virginia" or Cavaliers, had dominated the colony's politics and economy. They built large manor houses on their Tidewater plantations. By the 1730s, many were made of brick.