Long known to the Indian who used the Ohio and the Mississippi as highways for trade and war, this junction was first sighted by Europeans when Marquette and Joliet glided past in 1673. Ten years later La Salle explored the area and established France's claim to the Mississippi Valley. From that time on the confluence was recognized as a strategic site for settlement and fortification. Following the capture of Kaskaskia in 1778, George Rogers Clark stationed armed boats here to guard the Illinois country against attacks by the British or Spanish. In 1811 the New Orleans, the first steamboat to navigate western waters, lay at anchor here during three nights of the New Madrid earthquake. In April of 1861 Fort Defiance was established at the confluence to thwart Confederate invasion and blockade the trade of the South. From here General Grant launched his great flanking movement of the Cumberland and Tennessee Rivers, which began at Fort Henry and ended at Vicksburg, giving the Union complete control of the Mississippi.