Founded by Henri de Tonti in 1686 on the lower Arkansas River, Arkansas Post became the first European settlement in present-day Arkansas, the first permanent French outpost west of the Mississippi, and an important center of trade and diplomacy with the Quapaw. Repeatedly moved because of raids, foreign threats, and river erosion, it passed from French to Spanish control, saw the only Revolutionary War battle fought in present-day Arkansas, and later became part of the United States through the Louisiana Purchase. From 1819 to 1821 it served as the first capital of Arkansas Territory, and archaeological work has shown its enduring importance as a colonial and Quapaw site.