The world has never been more technologically advanced than it is now, but that doesn’t mean that some things haven’t been lost along the way. Many of the technologies, inventions, and manufacturing processes of antiquity have simply disappeared with the passage of time, while others are still not fully understood by modern day scientists. Some have since been rediscovered (indoor plumbing, road building), but many of the more mysterious lost technologies have gone on to become the stuff of legend. Here are ten famous examples.