Fire Temple in Isfahan is a remarkable memorial left from Sassanid dynasty which is located on the Mount Atashgah. It is one of the three fire temples remained from Iranian Ancient history in Isfahan. This archaeological wonder being located on the top of the hill, was first studied and examined by ‘Williams Jackson’, an American expert in the field of Iranian History. He recognized this monument as an Iranian fire temple. Later on, some Islamic specialists examined the structure and had the same idea. There are many controversial debates over the usage of this fire temple. Some believe that it was a palace belonging to Sassanid prince while some others considered it as a military castle. Its special situation, the plan of the monument and the building materials show the existence of a fire temple owning by a big temple. The fire temple in Isfahan includes 7 large windows and an entrance, which in old days, flames were flickering in every directions and recognized from far distances. Ancient texts have referred to the fire temple as ‘Mehrin’ as well as an ancient city with the same name. The fire temple was registered as a national heritage in 1951.