Among Western orientalists and travellers, the structure was first observed by Eugène Flandin and Pascal Coste, who noted its uniqueness in Iranian architecture.
Prior to Ernst Herzfeld studies of the structure, Terbal was mistakenly thought to be a descendant of the ziggurat, while some thought it is a fire temple, with the Holy Fire (Atar) being put at its top to avoid contamination with dust.

It is hypothesised that the structure may have been part of a government building and symbolised the divine and centralist kingship introduced by Ardashir I. It may have had practical military and civil uses as well, as the tower provided visual contact with some fortifications in the area, and/or may have been used as an observation tower to survey activities during the implementation of the planned scheme of the new city of Gor and the plain.
In fact, this grand scheme was centred in Terbal and continued the concentric and radiant pattern of the town, with traces of canals, paths, walls and field borders found up to 10 km distance from this central tower.

According to a newer study, the structure, as also described in medieval sources, may have functioned as a water tower, in such a way that water from nearby elevated sources would flow through tubes and Terbal's hollow core towards its dome, and from there it would be flowed to another tube to flow elsewhere in the town.
It is argued that it was not the only purpose of the structure, but it was also part of a temple of Anahita, the divinity of the Waters (aban).
Among Western orientalists and travellers, the structure was first observed by Eugène Flandin and Pascal Coste, who noted its uniqueness in Iranian architecture. Prior to Ernst Herzfeld studies of the structure, Terbal was mistakenly thought to be a descendant of the ziggurat, while some thought it is a fire temple, with the Holy Fire (Atar) being put at its top to avoid contamination with dust.
It is hypothesised that the structure may have been part of a government building and symbolised the divine and centralist kingship introduced by Ardashir I. It may have had practical military and civil uses as well, as the tower provided visual contact with some fortifications in the area, and/or may have been used as an observation tower to survey activities during the implementation of the planned scheme of the new city of Gor and the plain. In fact, this grand scheme was centred in Terbal and continued the concentric and radiant pattern of the town, with traces of canals, paths, walls and field borders found up to 10 km distance from this central tower.
According to a newer study, the structure, as also described in medieval sources, may have functioned as a water tower, in such a way that water from nearby elevated sources would flow through tubes and Terbal's hollow core towards its dome, and from there it would be flowed to another tube to flow elsewhere in the town. It is argued that it was not the only purpose of the structure, but it was also part of a temple of Anahita, the divinity of the Waters (aban).
Minar (Firuzabad)