The Mississippi Delta was destined to become the site of a big city. The Mississippi River was the method of transport for raw materials, people, and supplies for a large part of the U.S. and New Orleans became its sea port.
Three hundred years ago this spring, French colonials first began clearing vegetation to establish La Nouvelle-Orléans on the meager natural levee of the Mississippi River. At most 10 to 15 feet above sea level, this feature accounts for nearly all the region’s upraised terrain; the rest is swamp or marsh. One Frenchman called it “Nothing more than two narrow strips of land, about a musket shot in width,” surrounded by “canebrake [and] impenetrable marsh.”
Those two narrow strips of land were not enough for the growing city, so engineers went to work to make more land, by draining swampland and diverting water. The result of all that work is that now 50% of the city is below sea level. Read how this happened at The Atlantic.