Abstract
Ramhormoz city is located in Khuzestan province, southwest of Iran. The founding of Ramhormoz is attributed to the Sassanid kings in Islamic period texts. Based on archaeological surveys and excavations conducted in Ramhormoz, traces of settlements from prehistoric times to the Qajar era have been identified. The Aala River, as one of the most important rivers in this city, passes through the Ramhormoz plain and divides it into two parts, eastern and western. On the banks of this river, there are traces and evidence of Sasanian investment in the agricultural economy, such as tunnels and water supply canals. Recently, due to subsidence of the riverbed near Tall Bormi and south of Ramhormuz, part of the remains of a structure have been revealed. This study, for the first time, examined the relationship between this structure and evidence of Ramhormuz irrigation. In the absence of a comprehensive and independent study of the Ramhormuz plain irrigation system, such a study is all the more necessary The goals of this research are to chronologies the structure and understand its relationship with other evidence of plain irrigation in order to determine its function. In order to achieve these goals, the method of library studies and analysis of historical texts and findings of previous archaeological surveys was used, along with the analysis and review of findings from the author’s field survey of the river structure and open and covered channels of the Aala River. Determining the function of the newly discovered river structure as a dam-bridge and part of the Ramhormuz irrigation system to feed the southern canal known as Moradbeigi and provide the possibility of movement between the two parts of the plain, determining the Sassanid chronology of the Moradbeigi canal and the bridge structure based on its connection with the Sassanid sites of the western plain, are among the most important findings of this research.
Keywords: River Structure, Bridge-Weir, Sassanid, Aala River, Ramhormoz.

Introduction
The Khuzestan Plain was one of the most important centers of the agricultural economy during the Sasanian period, due to its fertile lands and important and large rivers. At least since the Sasanian period, whose economy was based on agriculture, the inhabitants of Khuzestan built complex systems of dams, canals and underground tunnels into the river valleys (Mousavi & Daryaee, 2012: 1082; Alizade et al., 2004: 70). Among the numerous water structures built on the rivers of Khuzestan during the Sassanid period, at least two remains are located in the Ramhormoz region: one is the ancient Jareh Dam on the Zard River, and the other is part of the remains of a structure that was revealed as a result of the author’s field survey in the bed of the Aala River. Archaeological research and excavations have been conducted on the Jareh Dam before it was flooded, which has led to the identification of architectural remains from the Sassanid and Islamic periods. However, no independent research has been conducted so far regarding the newly discovered river structure in the Aala River bed, as well as the water supply system of the Ramhormoz Plain. Only in the archaeological studies of Ramhormuz, there has been a brief mention of the existence of canals and aqueducts of the Aala River; The reason for this could be the recent and late discovery of the water structure on the Aala River bed. Therefore, such research can increase knowledge and understanding of the Ramhormuz irrigation system during the Sassanid period. The most important questions that this research intends to answer are: 1) What function or functions did the newly discovered structure in the Aala River bed have? 2) Based on what evidence can this structure be attributed to the Sassanid period? The authors hypothesize that this river structure was the remains of a bridge or a dam-bridge. In addition to comparing the architectural remains, if there is a connection between it and other evidence of Sasanian irrigation on the Ala River, it could be a structure from the Sasanian period. The problem of this research, unlike similar studies that mainly examine the relationship between irrigation evidence and existing bridges and dams on the rivers of Khuzestan in order to understand the mechanism and goals of water supply, is to first determine the function of the river structure (bridge or dam-bridge?) by proving the relationship with irrigation evidence and then determining the goals of water supply in addition, determining the possible chronology of this river structure based on its relationship with evidence of Sasanian irrigation of the Ramhormuz plain and architectural materials and remains is another goal of this research.

Discussion
One use of this river structure is as a bridge, because the Aala River divides the Ramhormuz plain into two parts, eastern and western. Given the similarity of the architectural materials, it seems that this bridge was a Sassanid bridge. Identifying the function of the dam-bridge for this structure depends on proving its connection with other evidence of irrigation of the Ramhormoz plain. In the north of the plain, on the eastern walls of the river are the Jubaji Tunnels and on the western walls are the Zirzard Tunnels, which are actually a type of river aqueduct. Given the large distance between the northern aqueducts and the location of the river structure’s discovery, as well as the location of the tunnels close to the riverbed, it is clear that this structure has no connection with the northern aqueducts of the Ramhormoz Plain However, in Henry Wright and Elizabeth Carter’s survey of the western plain of Ramhormuz, they mentioned Sasanian canals. One of these canals (the southern canal), now called Moradbegi, is located a hundred meters upstream of the structure, which proves that this structure was a dam-bridge. Of the 6 sites associated with the Moradbegi Canal, about 5 sites have Sassanid settlements, indicating that Moradbegi is a Sassanid canal. Since the end of this canal leads to three sites RH-8, RH-8, and RH-22S, it seems that the purpose of constructing the canal was to provide water for consumption at these sites, in addition to agriculture. This function is possible, according to the “Maqdasi” report, regarding the supply of water to the city of Ramhormuz from the northern canal. After supplying water to the city of Ramhormuz, the northern canal entered the agricultural lands of the western plain and was used to irrigate these lands

Conclusion
The most important evidence of Sasanian investment in the Ramhormuz region can be seen in the Jareh Dam area and around the Aala River. During the Sasanian period and thereafter, the inhabitants of this region created irrigation systems branching off the rebellious Aala River, enabling the exploitation of the river’s water for agricultural and irrigation purposes This system in the north of the Ramhormoz Plain included tunnels dug in the conglomerate river wall to irrigate the eastern part of the plain; and in the western plain, it included a number of irrigation canals. The southernmost canal, dated by Wright and Carter to Sasanian times, was fed from behind a bridge, the destroyed remains of which have recently been discovered in the riverbed near Tole Burmi. It seems that this fragmented and destroyed structure, considering its upstream Sasanian canal and the architectural typology, materials used, type of cutting and arrangement of stones used, belongs to the Sasanian period, which was used simultaneously as a bridge for passage between the eastern and western parts of the plain and as a dam to direct surface water and upstream of the structure to the Sasanian sites RH-9, RH-22S and RH-8 and agricultural lands, and had a dual use The construction of the Moradbeigi Canal, which was fed from behind the Aala dam-bridge, was in line with the policy of settling the agricultural population in large cities. Because, based on its size, the RH-9 site, apart from the Sassanid city of Ramhormuz, was a large population centre in the Ramhormuz plain that was abandoned in the post-Sassanian phase. Despite the importance of Ramhormuz in the constant exchanges between Fars and Khuzestan since prehistoric times, it does not seem that the Aala Bridge was a caravan bridge with strategic military and economic importance between different states, but rather a local structure or building that was built to manage the water of the Aala River in part of the Ramhormuz lands.