The iconic monument that today identifies the Old City of Jerusalem. First completed in 691, the Dome of the Rock is the only Islamic structure that has survived essentially as it had begun. It is not a mosque but a canopy over the rock on which, according to legends, Abraham sacrificed his son Isaac and on which Solomon's temple was built. It served, and continues to serve, essentially to assert Islam's supremacy over the Jews by its occupation of Judaism's holiest site, and over the Christians by its architectural dominance over the Church of the Holy Sepulchre. Both points are reinforced by the quranic inscriptions on the inside.
In an ironic twist, the technology for the golden dome —brass, layered with copper, nickel, and a 2-micron film of gold, and paid for by King Hussein of Jordan in 1994 — was supplied by an Irish Catholic firm, and the (present) beautiful tiles made by an Armenian Christian tilemaker from Aleppo.