- Vatican City
These four faces are also four sides of a square when the Holy of Holies is represented as a plane shape.
We know that the face is the means of identification. You might find it difficult identifying Jerusalem when shown photos of other buildings or other locations in Jerusalem. But you will certainly know that it is Jerusalem when shown the photo of Dome of the Rock. Although there are other buildings like Al-Aqsa Mosque and the Church of Holy Sepulchre, Dome of the Rock is the most prominent building in Jerusalem like the face of a human being is the most prominent part of his body. Therefore Dome of the Rock, the face of the City of Jerusalem, is the first face of the New Jerusalem.
Hagia Sophia, the magnificent citadel of Holy Wisdom, was the most prominent building in Constantinople. Therefore Hagia Sophia is the face or the means of identifying the place called Constantinople. Hagia Sophia is the second face of the New Jerusalem.
The Cube (the Kaaba) in the Great Mosque of Mecca is the most prominent place in Mecca. Therefore the Kaaba (the Cube) is the face of Mecca. The Kaaba is the third face of the New Jerusalem.
Saint Peter's Square (the Square) is the most prominent location in the Vatican City. In fact, Saint Peter's Square is synonymous to the Vatican City. Therefore Saint Peter's Square is the face of the Vatican City, and the forth face of the New Jerusalem.
All four faces are essentially the same thing: the Holy City. They are four different manifestations of the Holy City where God dwells.
Let the Rock = A, Holy Wisdom = B, the Cube = C, and the Square = D.
Holy of Holies = A = B = C = D