The MBM, "The largest small-scale working model in the world," is, well, a little strange.

BY TOM VANDERBILT

When I first heard that there was a giant topographical model of the Mississippi River basin near Jackson, Miss., I knew I had to see it. Give me a 1-to-100 scale model and I see the sublime. To me, small is beautiful, and the bigger the small, the better. This replica of the entire "gathering of waters" (as the word Mississippi means in Ojibwa) covered 40 acres of Delta lowland, 15 acres of which was solid concrete.

Through the 1960s, the "largest small-scale working model in the world" was open for tours and listed on tourist maps, but it took several phone calls before I could find anyone in the city government who even knew that Jackson owned this treasure. "Try the Department of the Interior," one befuddled clerk suggested. At the Jackson Department of City Planning, Tim Akers, after rifling through some folders, was able to tell me that the model was a state landmark and was on the "endangered" list issued by the Mississippi Heritage Trust in 2000. When I asked him about the model's condition, he said, "It's interesting, but decaying. And it's out in the middle of nowhere."

The model was built by the U.S. Army Corps of Engineers to replicate the third-largest river basin in the world, one that ranges across 1,250,000 square miles, spans 41 percent of the continental United States, and contains some or all of 31 states and two Canadian provinces. Begun in 1943 and mostly completed by 1966, at a horizontal scale of 1 to 2,000 and a vertical scale of 1 to 100, the Mississippi Basin Model (MBM in Corps par-lance) had miniaturized horizons so broad that its designers had to incorporate the curvature of the earth into their calculations. Every element of the river basin—including not only geographical features but also levees, railroad embankments, and the occasional bridge—was sculpted by hand, often in modeling clay, to match the actual contours.

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