Nishapur or Nishabur (pronunciation ; Persian: نیشابور, also Romanized as Nīshāpūr, Nīshābūr, and Neyshābūr from Middle Persian: New-Shabuhr, meaning "New City of Shapur", "Fair Shapur", or "Perfect built of Shapur") is a city in the Khorasan Province, capital of the Nishapur County and former capital of Province Khorasan, in northeastern Iran, situated in a fertile plain at the foot of the Binalud Mountains. It had an estimated population of 239,185 as of 2011 and its county 433,105. Nearby are the turquoise mines that have supplied the world with turquoise for at least two millennia. The city was founded in the 3rd century by Shapur I as a Sasanian satrapy capital. Nishapur later became the capital of Tahirid dynasty and was reformed by Abdullah Tahir in 830, and was later selected as the capital of Seljuq dynasty by Tughril in 1037. From the Abbasid era to the Mongol invasion of Khwarezmia and Eastern Iran, the city evolved into a significant cultural, commercial, and intellectual center within the Islamic world. Nishapur, along with Merv, Herat and Balkh were one of the four great cities of Greater Khorasan and one of the greatest cities in the middle ages, a seat of governmental power in eastern of caliphate, a dwelling place for diverse ethnic and religious groups, a trading stop on commercial routes from Transoxiana and China, Iraq and Egypt. Nishapur reached the height of its prosperity under the Samanids in the 10th century, but was destroyed by Mongols in 1221, and further ruined by other invasions and earthquakes in the 13th century. After that time, a much smaller settlement was established just north of the ancient town, and the once bustling metropolis lay underground—until a team of excavators from the Metropolitan Museum of Art arrived in the mid-20th century. They worked at Nishapur between 1935 and 1940, returning for a final season in the winter of 1947–48. What remains of old Nishapur region is a 3500-hectare "Kohandejh" area, south of the current city of Nishapur.