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The Marib Dam (Arabic:سد مأرب) blocks the Wadi Adhanah (also Dhana or Adhana) in the valley of Dhana in the Balaq Hills, Yemen. The current dam is close to the ruins of the Great Dam of Marib, dating from around the seventh century BCE. It was one of the engineering wonders of the ancient world and a central part of the south Arabian civilization around Marib.

The site of the great Dam of Marib (Sudd Marib) is upstream (south-west) of the ancient city of Marib, once the capital of the Kingdom of Saba'a, believed to be the kingdom of the legendary Queen of Sheba. The Kingdom of Saba'a was a prosperous trading nation, with control of the frankincense and spice routes in Arabia and Abyssinia. The Sabaens built the dam to capture the periodical monsoon rains which falls on the nearby mountains and so irrigate the land around the city.

Recent archaeological findings suggest that simple earth dams and a canal network were constructed as far back as 2000 BCE. The building of the first Marib dam began somewhere between 750 BCE and 700 BCE and took some hundreds of years to complete. (The Rulers of Sheba and Himyar Ali Yanouf Bin Dhamar Ali had his name carved into parts of the dam to mark its completion). The dam was of packed earth, triangular in cross section, 580 m in length and 4 meters high. It ran between two groups of rocks on either side of the river and was linked to the rock with substantial stonework. The dam's position allowed for a spillway and sluices between the northern end of the dam and the cliffs to the west. Around 500 BCE the dam height was increased to 7 meters, the upstream slope (the water face) was reinforced with a cover of stones, and irrigation was extended to include the southern side as well as the northern side.

After the end of the Kingdom of Sheba, possession of the dam came to the Himyarites in around 115 BCE. They undertook a further reconstruction, creating a structure 14 meters high with extensive water works at both the northern and southern ends - with five spillway channels, two masonry-reinforced sluices, a settling pond, and a 1000 meter canal to a distribution tank. These extensive works were not actually finalised until 325 AD and allowed the irrigation of 25,000 acres (100 km²).

Despite the increases in height, the dam suffered numerous breaches (recorded major incidents occurred in 449, 450, 542 and 548) and the maintenance works became increasingly onerous, the last recorded repairs took place in 557. In 570 or 575, the dam was again overtopped and this time left unrepaired. The final destruction of the dam is noted in the Koran and the consequent failure of the irrigation system provoked the migration of up to 50,000 people.

In 1986 a new 38 m high, 763 m long, earth dam was completed across the Wadi Dhana, creating a storage capacity of 398 million cubic meters. The dam site is located 3 km upstream of the ruins of the old Marib dam. The new dam was designed to store water for irrigating the Marib plains.

• A Study of the Marib Dam and It's Sluice System (115 B.C. - 575 A.D.)

Coordinates: 15°23′N, 45°14′E