Quote Originally Posted by Tinkerer View Post
Usually it is a result of magic slowly dying in that world. In the works of fiction where this trope came from it's because the world was implied to be OUR world just far far in the past.
Or in the distant future, with the artifacts being modern technology. Examples include Empire of the East, most of Vance's stuff, The Book of the New Sun, and any number of others. Sometimes you see riffs where it's on a spaceship (the Jacob's Ladder Trilogy) or a colony world (the Darkover series, Lord of Light). John Ring has a riff that catalogs the collapse of the high-tech civilization into magic-ish barbarism (the Council Wars). Mark Lawrence seems to be particularly fond of the trope, with all three of his published series to date (the Broken Empire, the Red Queens War, and the Book of the Ancestor) taking place in worlds where a technological civilization collapsed leaving behind wonders both magical and technological. For more examples than you could possibly need, see Ancient Advanced Humans, After the End, or Advanced Ancient Acropolis on TV Tropes.