Originally, Mount Zion was the scarp of rock on the southern tip of the ridge between the Kidron and Tyropoeon valleys. That cliff was an essential part of the fortress city occupied by the Jebusites who felt their stronghold, high in the Judean mountains, was impregnable. However, the tunnel that connected them to their water source, at the Spring of Gihon, was discovered by David. That tunnel provided a passageway under the walls of the city by which David captured the Jebusite fortress. David built his throne city between the two valleys and the City of David became known as Zion.
Now before Saul was appointed king of the tribes of Israel, the Philistines had captured the Ark of the Covenant. The Ark remained in the land of the Philistines for seven months and those who didn't die were smitten with tumours. Therefore they returned the Ark, carrying it outside the borders of Philistia to the neighbouring city of Kiriath-jearim.
After David became king and built his city, he transported the Ark from Kiriath-jearim to Zion. There he pitched a tent to house the Ark and a grand celebration ensued. Because David was surrounded on all sides by war, the construction of the Temple was left to his son, Solomon, who was blessed with a more peaceful reign.
King Solomon chose a hill north of the City of David called Mount Moriah as the site for the Temple. His purpose was to house the Ark of the Covenant in a permanent structure. The Shekinah Glory, which was the visible manifestation of God’s presence, dwelled above the mercy seat and between the two cherubim. After the construction was completed, Mount Moriah was called Mount Zion.
As the years past, the name Zion became synonymous with the city of Jerusalem.