Mehdishahr (formerly, Sang-e Sar or Sangsar) is a city in and capital of Mehdishahr County, Semnan Province, Iran.
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 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.
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.