Merv, oasis city of the Silk Road

In the Murghab oasis, successive walled cities of Achaemenid, Hellenistic, Sasanian and Islamic Merv grew beside one another on the Silk Road between Iran and Central Asia. Capital of the Seljuk sultan Sanjar in the 12th century, it may then have been the largest city in the world, until a Mongol army under Tolui destroyed it in 1221. Its ramparts, mausoleums and mud-brick manors span some two thousand years.