The Qanats of Ghasabeh (Persian: قنات قصبه‎), also called Kariz eKay Khosrow, is one of the world's oldest and largest networks of qanats (underground aqueducts). Built between 700 and 500 BCE by the Achaemenid Empire in what is now Gonabad, Razavi Khorasan Province, Iran, the complex contains 427 water wells with a total length of 33,113 metres (20.575 mi). The site was first added to UNESCO's list of tentative World Heritage Sites in 2007, then officially inscribed in 2016, collectively with several other qanats, as "The Persian Qanat".