Ahmad Sanjar was born in 1085 and ruled from Merv over the eastern reaches of the Great Seljuk Empire. His reign lasted four decades, during which he repelled invasions from the Ghaznavids in 1097 and Turkmen forces in 1098. But fortune turned against him. At the Battle of Qatwan in 1141, the Qara Khitai -- the Western Liao Empire -- handed Sanjar his first major defeat. In 1153, the Oghuz Turks captured him outright. He escaped three years later, in 1156, to find his province stripped bare by raiders. He died the following year, and his successor Muhammad ibn Aziz commissioned a tomb proportional to the grandeur of the man's reign.

The mausoleum that Muhammad ibn Aziz built is deceptively simple in form: a cube topped by a dome, standing 27 meters high with walls 14 meters tall and a footprint of 27 by 27 meters. Simplicity, though, was not the point. The interior was the focal point -- an ambitious double dome construction, the inner dome lined with blue glazed bricks, the drum buttressed at four points. A hexadecagonal structure surrounded the outer dome. The building was composed of terracotta, plaster, stucco, and brick, each material serving both structure and decoration. It was part of a larger complex including a mosque, a palace, and supporting buildings. Sanjar had previously commissioned a massive dam on the Murghab River; this tomb was the second great construction project of his patronage.

When Tolui's Mongol army took Merv in 1221 after a seven-day siege, they massacred the city's inhabitants, enslaved around four hundred artisans, and set fire to most of the city's buildings. According to the Arab historian Ibn al-Athir, the Mongols "set fire to the city and burned down the mausoleum of Sultan Sanjar, having dug up his grave in the search of precious objects." The fire destroyed much of the exterior brickwork and caused the outer dome to collapse. Merv was depopulated. The tomb sat in its ruined state for centuries, slowly deteriorating as wind and sand did what the Mongols had not quite finished. The first photographs, taken by V.A. Zhukovsky in 1896 and E. Cohn Wiener in 1926, show a collapsed dome and heavily damaged galleries.

Recovery came slowly. Soviet architect N.M. Bachinskii completed the first structural analysis during a 1937 restoration, unearthing the foundations of the adjoining mosque. Further Soviet work followed in the 1950s. A cement capping was added to the dome in 1996. In 1999, UNESCO declared the monuments of ancient Merv a World Heritage Site, and from 2002 to 2004 the Turkish government funded extensive repairs approved by UNESCO that strived to honor the original design. Despite these efforts, the tomb remains incomplete. The second story is gone. The turquoise outer dome that once caught the desert light is absent. The surrounding palace and mosque exist only as foundations. What survives is a monument to what was, and to the stubbornness of good construction.

Most secular funerary architecture from the Seljuk period did not survive. That the Tomb of Ahmad Sanjar endured made it enormously influential. Its doubled-dome design and emphasis on monumental interior space -- a departure from the tall, narrow funerary towers typical of its era -- shaped domed architecture through the Ilkhanid, Timurid, and Safavid periods. The Ilkhanid ruler Ghazan Khan visited Merv, saw the tomb, and was so struck that he built his own funerary complex at Shamb in deliberate imitation. Two domes at the Jameh Mosque of Isfahan drew on Sanjar's hexadecagonal design. The Dome of Soltaniyeh followed its move toward squatter proportions and grand interiors. As the first mosque-mausoleum combination on record, it established a template that became widespread across Islamic architecture.