![Cities in Flight - 2nd Hand](http://www.beyond-books.co.uk/cdn/shop/products/cities_{width}x.jpg?v=1592850719)
James Blish's galaxy-spanning masterwork, originally published in four volumes, explores a future in which two crucial discoveries - antigravity devices which enable whole cities to be lifted from the Earth to become giant spaceships, and longevity drugs which enable their inhabitants to live for thousands of years - lead to the establishment of a unique Galactic empire. It is technically four short novels in one omnibus and he did help create Star Trek too.