of the wadi and a rock shelf on the north. Its location a little downstream of the wadi’s narrowest point permitted space for a natural spillway and sluices. Around 500 b.c. a second 23-foot-high (7-meter) earth dam was built. It was triangular in section; both faces sloped at 45 degrees and the upstream side was faced with stone set in mortar. The final form of the Marib Dam was not built by the Sabaeans.

Late in the second century b.c. the Himyarites, a tribe from the extreme southwest of Arabia, established their capital at Dhafar and gradually absorbed the Sabaean kingdom, gaining control of South Arabia. They undertook the next major reconstruction of the Marib Dam, building a new 46-foot-high (14-meter), 2,350-foot-long (720-meter), stone-faced earthen wall, incorporating sophisticated hydraulic systems. It was nearly 200 feet (60 meters) thick at the base, built on a stone foundation, and created a lake that was probably 1.5 square miles (4 square kilometers) in area. At each end of the wall there were sluices, constructed with what has been described as the “finest ancient masonry … in Arabia,” through which water was channeled to extensive irrigation networks on both sides of the valley floor. The southern sluice system had a 10-foot-wide (3.5-meter) spillway about 23 feet (7 meters) below the top of the dam. The northern system included a spillway and a massive channel outlet between the spillway and the earth wall. It carried water via a 3,300-foot-long (1-kilometer), 40-foot-wide (12-meter) stone-lined earthen conduit, rectangular in cross section, to a distribution point that fed 12 irrigation canals. The discharge flowing into the conduit was controlled by a pair of gates; it also passed through a large settling basin.

When the Romans began to trade with India directly via the sea routes, the South Arabian economic monopoly was broken. The overland route declined, and social structure began to disintegrate. The Himyarite dynasty was toppled by an Ethiopian invasion in a.d. 335, reestablished toward the end of the fourth century, and again overthrown by the Ethiopians in 525. The Himyarites were absorbed into the wider South Arabian population.

The Marib Dam was regularly breached, usually by overtopping, during the extreme floods that occurred about once in fifty years. Just as regularly—for example, in a.d. 450 and 542—substantial repair work was undertaken. But when it was overtopped in 575, it was not repaired. Its final destruction was later recorded in the Koran (632–650), attributed to the judgment of Allah: “But they turned aside, so We sent upon them a torrent of which the rush could not be withstood, and in place of their two gardens We gave to them two gardens yielding bitter fruit. …” There is also a Yemeni proverb, “The Marib dam was destroyed by a mouse.’ Archeologists and engineers attribute its collapse to lack of adequate, regular maintenance or to the gradual failure of the foundation. Whatever the case, deprived of their water supply, the lifeblood of their crops and gardens, thousands of people from Marib returned to the nomadic life or migrated northward. The collapse of the dam expedited Bedouin insurgence from the Najd, and Islam was introduced around 630.

In December 1986 a new 125-foot-high (38-meter) earth dam was officially inaugurated. It closes off the Wadi Dhana a little under 2 miles (3 kilometers) upstream of the old dam site. Like its ancient predecessor, it was designed to impound water for irrigating the Marib plains; a 12-square-mile (30-square-kilometer) lake with almost a capacity of 437 million cubic yards (400 million cubic meters) has transformed 45,000 acres (18,000 hectares) of desert into productive farmland.

Further reading

Grolier, Maurice J. et al. 1996. Environmental Research in Support of Archaeological Investigations in the Yemen Arab Republic, 1982–1987. Washington. DC: American Foundation for the Study of Man.

Knutsson, Bengt, et al., eds. 1994. Yemen, Present and Past. Lund, Sweden: University Press.

Schnitter, N. J. 1994. A History of Dams: The Useful Pyramids. Rotterdarn: Balkema.

Masjed-e-Shah (Royal Mosque)

Isfahan, Iran

The Royal Mosque, or Masjed-e-Shah (now known as the Masjed-e-Imam), was the major legacy of the Safavid Shah Abbas I (1587–1628), sometimes called Abbas the Great, who established Persia as a unified