Deledrius wrote:It's a bit hard to raise the ground level of a city that has buildings in it already.
Not at all, it was done in Seattle...
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[...] Speidel ultimately did find the remains of the city consumed in the Great Seattle Fire of 1889, a town founded on mostly soggy tideflats whose streets would, whenever the rains came, bloat deep enough with mud to consume dogs and small children.
After the fire, which destroyed some 25 square blocks of mostly wooden buildings in the heart of Seattle, it was unanimously decided that all new construction must be of stone or brick masonry. The city also decided to rise up from the muck in which its original streets lay.
The city built retaining walls, eight feet or higher, on either side of the old streets, filled in the space between the walls, and paved over the fill to effectively raise the streets, making them one story higher than the old sidewalks that still ran alongside them.
Building owners, eager to capitalize on an 1890s economic boom, quickly rebuilt on the old, low, muddy ground where they had been before, unmindful of the fact that their first floor display windows and lobbies soon would become basements. Eventually, sidewalks bridged the gap between the new streets and the second story of buildings, leaving hollow tunnels (as high as 35 feet in some places) between the old and new sidewalks, and creating the passageways of today’s Underground.
http://www.undergroundtour.com/about/history.html
