Cube of Zoroaster in the front large rock-cut tombs made for Achaemenid kings, Naghsh-e Rostam, Fars Province

The Cube of Zoroaster (also known as Ka'ba-ye Zartosht) is a 5th century BC Achaemenid-era tower-like construction at Nagsh’e Rostam, just northwest of Persepolis, in Fars Province. The structure is not actually a Zoroastrian shrine, nor are there reports of it ever having been a pilgrimage site. The structure, which is a copy of a sister building at Pasargadae, was built either by Darius I (r. 521–486 BC) when he moved to Persepolis, by Artaxerxes II (r. 404–358 BC) or Artaxerxes III (r. 358–338 BC). The wall surrounding the tower dates to Sassanid times.

 

The square tower is constructed of white limestone blocks, that - unlike those of the sister building - are held in place by iron cramps. Mortar was not used in its construction. Each side of the building is 7.25 meters wide. The 12.5 meter high structure has a slightly pyramidal roof and stands on a 1.5 meter high three-stepped plinth. Each face of the building is decorated with slightly recessed false windows of black limestone.

 

The structure has one square inner chamber, 5.70 meter high and 3.70 meter wide, access to which is through a doorway with a decorated lintel in the upper half of the tower. The chamber was once accessible by a flight of steps, only the lower half of which has survived. The 1.70 meter wide and 1.90 meter high door was of solid stone that was originally firmly closed but has since disappeared.

 

From a reference to fire altars in a Sassanid-era inscription on the building it was inferred that the structure was once a fire altar, or perhaps as an eternal-flame memorial to the emperors whose tombs are located a few meters away. This theory has however since been rejected since the lack of cross-ventilation would have soon choked the flame. A later opinion suggested that both it and its sister building were safety boxes for the royal flags and other important belongings of the governing kings. Some experts believe that the monument was the home of a complete copy of the Avesta which had been written on 12,000 leather parchments.

 

Iranian archaeologist Reza Moradi Ghiasabadi has presented his own theory and described the monument as the world's most unique calendrical and astronomical observatory. According to him the month, day and even certain times of the day can exactly be determined by the sunlight shed on the structure and its resulting shadows. 

 

Furthermore he believes it had been used for matters such as daily needs, establishing the time of cultivating crops, collecting taxes and determining significant holidays throughout the year. For example at the beginning of Farvardin and Mehr, the structure’s shadow falls on the 27th step, at the beginning or Ordibehesht and Shahrivar on the 29th step and so on.

 

The Cube of Zoroaster bears a Sassanid era inscription explaining the historical events during the reign of the Sassanid king Shapur I (241-272 CE). The trilingual inscription, written in the Sassanid and Parthian dialects of Middle Persian and ancient Greek, describes the war between Persia and Rome in which Shapur I defeated Valerian, who was captured in 260 and died in captivity.

 

The Sassanid-era wall surrounding the structure has four inscriptions dating to the 3rd century. The trilingual inscription of Shapur I (241–272) is on the eastern (Middle Persian text), western (Parthian text) and southern (Greek text) walls. A Middle Persian inscription is below Shapur's on the eastern wall.

 

Today, some scholars also consider the structure to be an Achaemenid royal tomb, and it has been observed by F. Weissbach and A. Demandt that both the Cube of Zoroaster and its sister building at Pasargadae "more closely correspond to the description of Cyrus the Great's tomb than does the monument in Pasargadae which is commonly attributed to this king.