"Floating Gardens" - The Aztecs once fed 200K people in inarguable swampy land by creating floating gardens they farmed extensively.
Chinampas, used by The Aztecs and other mesoamerican cultures. Artificial islands that have the potential to produce up to 7 rounds of crops per year.
Chinampa (Nahuatl: chināmitl [tʃiˈnaːmitɬ]) is a method of Mesoamerican agriculture which used small, rectangular areas of fertile arable land to grow crops on the shallow lake beds in the Valley of Mexico.