The oldest buildings in downtown Chattanooga, Tennessee, have strange things underground. Basements have windows and doors that go nowhere. Most are bricked up, but you can tell what they were. Construction workers have found cut tree stumps eight feet down. Sometime between 1875 and 1905, the entire downtown area was raised up a floor, and the buildings' second floors became their first floor. Unlike some other such towns, you can't explore the abandoned level, because the roads between the buildings were filled in, and the spaces are private property anyway. The strange thing is, city records do not tell us when it happened, or why- although they had reasons. The city had occasional floods and a drainage problem, and then there was yellow fever.
More motivation arrived in the summer of 1878, when yellow fever spread across the Mississippi River basin, striking its victims with jaundiced skin and black vomit, and killing thousands. In Chattanooga, 140 people in the city of 12,000 died.
People at the time didn’t know the true carrier of the disease, Aedes Aegypti mosquitoes, which can spread the Zika virus of today. But Chattanooga’s then-Registrar of Vital Statistics, J. H. Vandeman, was onto something when he wrote: “The more filth, the more yellow fever; the lower the ground, the poorer the drainage and water supply, there you would find this disease the worst.”
Whenever it happened, changing the ground level helped with flooding, sewer function, and general swampiness. Read what we know about Chattanooga's mysterious urban redesign at Atlas Obscura.
(Image credit: Daniel Jackson)
http://www.chicagotribune.com/news/nationworld/politics/chi-chicagodays-raisingstreets-story-story.html
"A popular story of the time [1850s] had it that a passerby came upon a man whose head and shoulders protruded from the muck in the middle of the street. "Can I help?" asked the passerby. "No, thank you," replied the man. "I have a fine horse under me.""