There will be a metropolis with a triangular roof

Richard Buckminster Fuller, Shoji Sadao : Architect
Fuller and Sadao designed this crystalline pyramid for Matsutaro Shoriki, a Japanese financier. The form is a tetrahedron (a four-sided triangular solid), with each edge measuring two miles. The buoyant metropolis was designed to accommodate one million citizens in 300,000 apartment units, and it even includes a huge interior harbor. Fuller, who spent his career searching for "ever higher performance with ever less investment of material resources," envisioned Tetrahedron City as an efficient response to two major problems of architecture and urban planning: construction costs and land acquisition. The tetrahedral composition with an aluminum octet truss system makes the structure's enormous size feasible and economical. Additionally, by designing the city to float at sea (in this case in Tokyo Bay), the cost of real estate is diverted.
Fuller and Sadao's radical urban proposal was never built.

MoMa, The Collection