Archaeologists launched fourth archaeological excavation season in the Zahhak Castle historical site.

A report released by the media department of Iran's Cultural Heritage Organization (ICHO) said that archaeologists look for remains of a single pillar base of Parthian era.

The head of the archaeological group, Javad Qandgar, said that in the first phase of excavation, a parlor made of brick, mortar and plasterwork, which was decorated with human figures as well as plant and geometrical motifs, was unearthed in the castle.

The castle is likely to have been a government building or a fire-temple belong to the third Iranian dynasty, the Ashkanids (Parthians).

"Zahhak Castle historical site was a defensive and military stronghold, but nothing is known on its date of construction and the reason for selection of its name.

The ancient site which is located 16 kms to the east of Hashtroud, in East Azarbaijan province, was first unearthed by a British colonel in 1830.