Kiyasar

The city of Kiyasar is located 70 km southeast of the city of Sari, at an altitude of 1,378 m above sea level, at north 36°14'16" and east 53° 32' 16".
Kiyasar is the center of Chahar Dangeh District. It used to be flourishing in the past and was considered a primary commercial and scientific center in the region. The surround villages used to provide their requirements in Kiyasar and came over there for educational purposes.
Once the coal mine in Kiyasar was shut down, it's population decreased and as a result of the villagers migration the city is not as prosperous as in the past.

But hopefully with the establishment of a cement factory in the village of Tarkam and thriving of the industrial township of Chahar Dangeh, Kiyasar will again boom like the old days.
Kiyasar in the wordbook of Dehkhoda

The town of Kiyasar is the center of Chahar Dangeh District in the city of Sari, 72,000 Gaz, a distance unit, southeast of Sari and 84,000 Gaz from Damghan. It's a mountainous area with a mild climate. 2,300 people reside in there. ( Taken from the Geographical Index of Iran, volume 3).

The location

Kiyasar lies within a valley surrounded by mountains on each side and only the northwest lacks a mountain and is connected to Kiyasar Plain.
Kiyasar extends south to Zar Kuh and Kal Sar mountains, west to Shah Kuh, east to Kal Posht and Fatla (which apparently is another version of Fathollah) mountains and north to the mountains of Ajir Lengeh, Nastar Nastara, Asb Zin and Malmali.

Climate

It is mild in Kiyasar in summer and very cold in winter.
Kiyasar was turned into a city in 1372, solar calendar, and its municipality was established.

Appellation

On why it is called Kiyasar, in the book titled Tabarestan's History, first volume, by Ardeshir Barzegar, p.36 and the book Mazandaran's History which is a manuscript by Sheikh Seifollah Yasari, (he was the first teacher of Chahar Dangeh in 1304, solar calendar ) p.13 as well as in the book called 2000 -year History of Sari written by Hussein Islami pp. 35,36, 37 it is summarized:
Kiyus, Tabarestan's ruler, was the older son of Ghobad, and his government was centered in Gharenkuh and Hezar Jarib. Kiyus built a city in the current place which was then called Kiyus Sara, literally Kiyus Home, and after his death the name changed to Kiyasara and then to Kiyasar.
The first official governor of Chahar Dangeh, Hassan Eezam Ghodsi with a nickname of Eezam Alvezareh who was appointed by Vosugh Aldoleh and came to Kiyasar in 1298, solar calendar, mentions the name as Kiyasara in all his memories. It indicates that it was still known as Kiyasara.
A couple of castles encompass Kiyasar including Shahrestan, Nastar Nastara, Zinden etc. Shahrestan which is still habitable is indeed old.
On the city, Sheikh Seifollah Yasari in his book, Mazandaran's History on page 13 writes:
Since I was born in Hezar Jarib, I lived quite some time in Kiyasar but I did n't see anything noteworthy other than a bathhouse (The bathhouse is now destroyed and is replaced by a cooperative business.) whose date of construction is not clear but the form of the structure shows it is quite old.
It is believed that the bathhouse was built by Kiyus, the son of Ghobad of the Sassanid.
Some of the locals and well-informed people believe that the bathhouse was first a fire temple and then its function changed.