The Sultan Sanjar Mausoleum is the most complete monument left at Merv. It was built in 1157 for the Seljuk ruler Ahmad Sanjar, who had died after years of imprisonment by his own subjects. The structure is a 38-metre-cube of brick topped by a 30-metre dome — at the time of its completion, one of the largest brick domes in the world. The outer dome was clad in turquoise tiles that could be seen from a day's journey away; that outer skin is gone, leaving the inner dome exposed.
Architecturally the mausoleum is the bridge between the brick architecture of Khorasan and the great tiled monuments of Timurid Samarkand a century later. The Mongols looted but did not destroy it in 1221, and it has stood through eight hundred years of earthquakes and desert wind. A modern Turkmen restoration has stabilised the dome and added a small turquoise band to suggest the original colour.