To some, western civilization in the United States started in the middle of an Arkansas swamp near Blackton, Arkansas, -- the reference point from which lands west of the Mississippi River were first measured.
After Thomas Jefferson bought Louisiana and Lewis and Clark explored it, the nation's land office sent a lesser known but just as important duo -- Robbins and Brown -- into southern Arkansas to begin surveying the 830,000-square-mile purchase.
Their first measurements established land grants for soldiers from the War of 1812. Eventually, plots throughout the Louisiana Purchase could be traced to a pair of gum trees between the Arkansas and St. Francis rivers.
Surveys break down land into a grid so each property can be identified by how far it is from a starting point. The federal land office had already determined that Louisiana lands -- bought 200 years ago this year -- would be measured from a spot between the Arkansas and St. Francis rivers, but needed surveyors to establish that point.
Robbins worked north from the mouth of the Arkansas and Brown worked West from the mouth of the St. Francis. They met in a cypress and tupelo gum swamp and marked a pair of gum trees to establish their base line and meridian.
From here, in general, the rest of the new American frontier was laid out in six-mile squares known as townships.
America's first meridian helped define land in Ohio; the Arkansas site marks the first meridian established west of the Mississippi River and is the primary reference point for land as far north as Canada and as far west as the Montana-North Dakota line. Later meridians were established farther west as settlement progressed -- except for Texas, whose land distribution varied under its multiple governments.
Each township is further divided into squares one mile on each side and, from there, property can be easily cut up into 160-acre tracts. The terms "the north 40" and "40 acres and a mule" are directly tied to how tracts were developed.