Wikipedia
Mehdishahr (, also Romanized as Mehdīshahr; formerly, Sang-e Sar (, also Romanized as Sang-i-Sar and Sangsar) is a city in and capital of Mehdishahr County, Semnan Province, Iran. At the 2006 census, its population was 20,581, in 5,473 families.
Mehdishahr is located 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 primary religious belief in the area now is Shi‘ite Islam, but before the Islamic Revolution, there were many Bahá'ís 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 Mahdishahr as if to signal its imposed pure Muslim identity. Mahdi is the Shia Muslim hidden Imam and Shahr means town in Persian, so Mahdishahr literally means town of Mahdi.
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.