Band-e Kaisar

The Band-e Kaisar (), Pol-e Kaisar ("Caesar's bridge"), Bridge of Valerian or Shadirwan was an ancient arch bridge in Shushtar, Iran, and the first in the country to combine it with a dam. Built by a Roman workforce in the 3rd century AD on Sassanid order, it was also the most eastern Roman bridge and Roman dam, lying deep in Persian territory. Its dual-purpose design exerted a profound influence on Iranian civil engineering and was instrumental in developing Sassanid water management techniques.

The approximately 500 m long overflow dam over the Karun, Iran's most effluent river, was the core structure of the Shushtar Historical Hydraulic System (سازه‌های آبی شوشتر) from which the city derived its agricultural productivity, and which has been designated by the UNESCO as Iran's 10th World Heritage Site in 2009. The arched superstructure carried across the important road between Pasargadae and the Sassanid capital Ctesiphon. the dam bridge remained in use until the late 19th century.

History and significance

The story is related by the Muslim historians Tabari and Masudi in the 9th and 10th centuries. Although their novel-like narrative cannot be ignored, the historical presence of the Romans is corroborated by modern local names, such as "Roumischgan" for a nearby village, and a Lurs tribe by the name of "Rumian". Moreover, local tradition ascribes to Roman settlers the origin of a number of trades, like the production of brocade, and several popular customs.

Modelled on the Roman example, the integration of a bridge superstructure into dam design became a standard practice of Iranian hydraulic engineering which lasted until about 1000 AD, when it culminated in the still existing Band-e Amir at Shiraz.

Construction

Shushtar lies on a rocky plateau above the Karun, Iran's most effluent river. An early dam, built by the Sassanids to divert water for the town and its extensive irrigable hinterland, did not work properly. The irrigation scheme put into effect after the arrival of the Roman labour force included three steps: First, the river was redirected towards the Ab-i Gargar, a channel which branches off the Karun at a point upstream of the dam construction site, rejoining the main river some 50 km south; the island it forms, called Mianâb ("Paradise"), is known for its orchard plantations.

Then, the Band-e Kaisar was built across the dried-up riverbed, with its foundations following a winding course in search for solid strata of sandstone. As the water flowed permanently over the top, the hydraulic structure conforms to the definition of a weir rather than a dam., but was most likely in the order of 3−4 m, which was enough to supply water for the irrigation conduits on both banks during the dry season. Despite its modest height, the weir wall was quite thick (9−10 m) in order to accommodate the arcaded superstructure.

On top of the weir, a roadway supported by originally at least forty arches ran along its entire length of around 500 m. The typical clear span of the Pol-e Kaisar was between 6.6 and 9 m.

The facing of the piers and the foundation consists of cut sandstone blocks bond by mortar and joined by iron clamps; the interior was filled with Roman concrete, a building technique also observed in the Pa-i-pol bridge. One former Persian name of the dam, "Shadirwan", derives from this paving. The time it took the Roman labour force to complete the ancient Shushtar hydraulic complex is variously reported as spanning three to seven years.

The site has been referred to as "a masterpiece of creative genius" by UNESCO. Along with the hydraulic works, it also includes Selastel Castle and a tower for water level measurement, as well as a series of water mills.

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