Kuh-e Khwaja is a complex 30 kilometers southwest of Zabol in the eastern part of Sistan-Baluchestan Province, very near the Afghan border.
The main ruins are on the southeastern promontory of a high hill overlooking the marshes of Lake Hamun (the historical Lake of Zereh) in the delta of the ancient Hirmand River. This small mountain juts out into the lake and is an island for most, or at least some, of the year.
Soroor Ghanimati has written about how she took part in the local field survey in 1995. There is a single path of access to the upper slopes of this hill through the neglected ruins of an ancient town. There’s a remarkable array of buildings and fortifications, including a citadel, known as Ghagha-Shahr, housing one of the only surviving fire temples within a major pre-Islamic monument.
This temple is on a terrace beyond high walls, protected by two forts: known as Kok-e Zal and Chehel Dokhtaran.
It is still inadequately documented – even though there were excavations by Aurel Stein (in 1915-1916), and then Ernst Herzfeld, and then Giorgio Gullini (in a short expedition in 1960).
Herzfeld tentatively dated the palace complex to the 1st century CE, that is, within the Arsacid period (248 BCE-224 CE). He later revised his estimate to a later date and today the Sassanid period (224-651 CE) is usually considered to be more likely.
Three bas-reliefs on the outer walls that depict riders and horses are attributed to this later period. See more images here.