| Official Name: | Mehdishahr |
| Native Name: | Persian: مهدیشهر |
| Settlement Type: | City |
| Pushpin Map: | Iran |
| Subdivision Type: | Country |
| Subdivision Name: | Iran |
| Subdivision Type1: | Province |
| Subdivision Name1: | Semnan |
| Subdivision Type2: | County |
| Subdivision Name2: | Mehdishahr |
| Subdivision Type3: | District |
| Subdivision Name3: | Central |
| Population As Of: | 2016 |
| Population Total: | 24485 |
| Population Density Km2: | auto |
| Timezone: | IRST |
| Utc Offset: | +3:30 |
| Coordinates: | 35.7144°N 53.3569°W |
| Coordinates Footnotes: | [1] |
| Area Code: | +98 (232) |
Mehdishahr (Persian: مهدیشهر), previously Sangsar, is a city in the Central District of Mehdishahr County, Semnan province, Iran, serving as capital of both the county and the district.[2]
Sangsar area has an old history which goes back to 1st millennium BC. First inhabitants of Sangsar used to worship moon and stars. There are some theories about Sangsar name; One of them emphasizes about a Saka origin and suggests the name used to be Sakasar or Saksar which means Saka (scythian) settlement.
The primary religious belief in the area now is Shi‘ite Islam, but before the Islamic Revolution, there were many followers of the Baháʼí Faith in Sangsar, who had to migrate from the city after the revolution, due to a wide range of persecutions. As for other towns of Iran, the name has thus been changed by the Islamic authorities into Mehdishahr as if to signal its imposed pure Muslim identity. Mahdi is the Shia Muslim hidden Imam and Shahr means town in Persian, so Mehdishahr literally means town of Mahdi.
At the time of the 2006 National Census, the city's population was 20,581 in 5,473 households, when it was in the former Mehdishahr District of Semnan County.[3] The following census in 2011 counted 19,854 people in 5,705 households,[4] by which time the district had been separated from the county in the establishment of Mehdishahr County. Mehdishahr was transferred to the new Central District as the county's capital.[2] The 2016 census measured the population of the city as 24,485 people in 7,679 households.[5]
Mehdishahr is on the southern slopes of the Alborz mountains. Here, the chain of Alborz mountains is very close to the desert of Dasht-e Kavir. Sangsar, specially the northern part of it, is completely mountainous with cold winters, heavy snowfalls but with mild summers. The distance between Sangsar city and Semnan city is 20 kilometers. The altitude is about 1630 meters above sea level.
The most important network of roads consists of Semnan to Sangsar to Shahmirzad to Fooladmahale axis which connects these places with the city of Sari. This road connects the two provinces of Mazandaran and Semnan.
Sangesar has signed the treaty of city twinning with the following cities: