Hernando de Soto, a Spanish explorer, is noted as the first European explorer to reach the Mississippi River. de Soto, along with 400 of his troops, discovered the river on May 8, 1541, according to the History Channel's official website. The group crossed the river just to the south of what is now Memphis, Tenn.
The area around the Mississippi River was dangerous for de Soto and his men as Native American tribes set up a patrol with war canoes. As a result, they crossed the river in the middle of the night, to avoid a confrontation with the natives.
After crossing the Mississippi River, the Spaniards traveled to what is now present-day Arkansas and Louisiana to continue their search for riches. They would later turn back to the river where de Soto would die on May 21, 1542.
Following de Soto's death, new commander Luis de Moscoso took the troops into north Texas before again returning to the river. Eventually, the troops built rafts and took the Mississippi River towards the Texas coast before setting sail for Veracruz, Mexico.
Later, the Mississippi River became the official border between the Spanish and British Empires following the signing of the Treaty of Paris in 1763. Spain's land fell to the west of the river, while Great Britain controlled everything on the east side of the river.