the only entrance door of a structure with a heavy and two-panel door, makes it clear that its content should be kept safe from robbery and pollution. Fireplace Engelbert Kaempfer first proposed the assumption of being a fire temple or fireplace; and following him, James Justinian Morier and Robert Ker Porter supported the view in the early nineteenth century. The southwestern corner of the chamber is blackened by smoke; and has caused the assumption that the holy fire was glowing in there. In the following years, Ferdinand Justi, Ghirshman, Schmidt and some others supported the hypothesis of Ka'ba-ye Zartosht being a fireplace. One of the reasons of this group is that Darius I says in the Behistun Inscription (First column, 63): "...I rebuilt the temples that Gaumata had destroyed. I returned the pastures, flocks, slaves and houses that Gaumata had taken to the people..." Thus, there were some "temples" in the periods of Cyrus II and Cambyses II that Gaumata destroyed and Darius rebuilt them the same way; and since "Solomon's Prison" in Pasargadae is belonging to the first Achaemenid era and destroyed, and its exact copy was built in Naqsh-e Rustam in Darius's period, it should be concluded that those two structures are the mentioned temples in the Behistun Inscription; and since any temple in Persia during Darius's period could not be anything other than the holy fire, those were all fireplaces; besides, Ka'ba-ye Zartosht has been conserved well even after the Achaemenid era and was not surrounded by soil and stones; and in the beginning of the Sasanian era, Shapur I composed the most important document of the Sasanian history on it and Kartir wrote a religious document on it. These show that the structure was religiously important. On the other hand, a structure is drawn on the coins of some Persian kings like those of Otophradates I that is a fireplace and the royal fire was kept above or inside it; and since the structure has a two-stair platform and its two doors are like Ka'ba-ye Zartosht and the center of the Persian kingdom was also in the city of Istakhr, it is the very Ka'ba-ye Zartosht that is drawn on their coins; and on the ceiling of this structure are put three fireboxes and the Persian king is standing in a praying posture in front of it. However, these reasons can not be true, for "Ayadana"