imaginary city built in air, 1830, translating Aristophanes' Nephelokokkygia in "The Birds" (414 B.C.E.). Cloud-land "place above the earth or away from the practical things of life, dreamland, the realm of fancy" is attested from 1840.
It is clear that none of the unfortunate people, perhaps at this moment on board, can stand upright, but that they must sit down, and contract their limbs within the limits of little more than three square feet, during the whole of the middle passage. I cannot compare the scene on board this vessel, to any other than that of a pen of sheep; with this difference only, that the one have the advantages of a wholesome air, while that, which the others breathe, is putrid. [Thomas Clarkson, "An Essay on the Slavery and Commerce of the Human Species," 1788]