Floating raft is a land-based building foundation that protects it against settlement and liquefaction of soft soil from seismic activity. It was a necessary innovation in the development of tall buildings in the wet soil of Chicago in the 19th century, when it was developed by John Wellborn Root who came up with the idea of interlacing the concrete slab with steel beams. The earliest precursor to the modern version may be the concrete rafts developed for the building of Millbank Prison in 1815 by Robert Smirke.