Zevachim 117 - The Three Camps
When the Jews lived in the desert, their encampment was divided into three areas: the Tabernacle, or the Camp of the Divine Presence, the Levite Camp, and the Israelite camp. Corresponding to these, in the times of the Temple there were the Temple, the Temple Mount, and Jerusalem.
Each area had its laws. A Metzora (spiritual leper) may not enter the Israelite camp, that is, Jerusalem at the time of the Temple, and the encampment at the time of the desert. An accidental murder was exiled to the Levite Camp, and in the time of the Temple, to one of the cities where the Levites lived. If a Levi murdered by accident, he had to be exiled to another Levite city, but if we moved from one neighborhood to another, this was sufficient. One who was ritually impure because of contact with a dead body could enter the Levite Camp (Temple Mount), but not the Temple proper.
Art: Eugène-Alexis Girardet - Bedouins In The Desert