Aflaj.

"Aflaj" is the plural of "Falaj", which means "split into parts" in classical Arabic.
This irrigation system effectively divided the water among all the inhabitants; it flowed by gravity from their original sources to homes and cropland. The complex included watchtowers to protect it, but also mosques and other buildings.[2]

In 2006, five Aflaj Irrigation Systems of Oman were added to the UNESCO list of World Heritage Sites.