Megascale engineering (or macro-engineering) is a form of exploratory engineering concerned with the construction of structures on an enormous scale. Typically these structures are at least 1,000 kilometers in length—in other words, at least 1 megameter, hence the name. Such large-scale structures are termed megastructures. Astroengineering is the extension of megascale engineering to megastructures on a stellar scale or larger, such as Dyson spheres, Ringworlds, and Alderson disks.