Finding a red cow that meets all the halachic requirements of a parah adumah was a rare event in Temple times. In fact, from the construction of the Tabernacle through the era of the Second Temple — a period of over 1000 years — only nine such cows were found (Parah 3:5). Since this opportunity came along so infrequently, extreme care was taken to ensure that it was prepared in the utmost sanctity. One of these requirements is that the Kohen who would handle the ashes of the cow must be quarantined within a dedicated chamber in the Temple, and denied all human contact for fear of contracting tumah, for seven days.
The Chamber of Shushan Habirah [the Capital] served as the repository for two different measuring sticks of the amah. In the northeast corner was a measuring stick that was half a fingerbreadth longer than a standard amah of six handbreadths and in the southeast corner was a stick that was a full fingerbreadth longer than a standard amah. This chamber had a depiction of the city of Shushan on its outer wall and this feature gave the chamber its name.