The separation wall, which is equally loathed by the Left for its ostensibly racist intentions (and by some, I fear, because it successfully interdicts suicide bombers) and by the Right because it threatens to permanently secede Israel proper from the West Bank and thus destroy any possibility of a Complete Land of Israel, is just visible on the hilltops southeast of the Old City. In this photo, its the gray line snaking through the trees on the hilltop just to the right of the buildings.
Jerusalem, of course, has a long and venerable tradition of walls. Like most ancient cities, it spent most of its history behind walls of various kinds which -- like this one -- were generally used to keep its enemies out. In ancient times, walls also served a psychopolitical purpose. A city which built walls was declaring itself to be big, rich, and important enough to be protected. The first act of a conquering empire was usually to tear down the walls of a vanquished city, thus achieving the practical advantage of reducing the city's defenses and thus discouraging rebellion, and the equally important psychological advantage of declaring to both the residents and the world outside that the order of things had been permanently shifted. Of course, nothing is permanent, especially in Jerusalem, and walls were as often rebuilt as they were destroyed, one of the most famous being the rebuilding of Jerusalem's walls after the first Return to Zion under Ezra and Nechemia, coinciding with the first rebuilding of the Temple.
Like the Temple, the walls of Jerusalem were reconstructed several times, as this likely speculative map of 1st century Jerusalem shows, before the Romans finally razed them -- and the rest of the city -- to the ground in its classic scorched-earth style of putting down rebellions.
Of course, Jerusalem did not remain without walls for long. A series of conquerers, including Suleiman the Great, who built much of the wall which now surrounds the Old City, did their bit to keep Jerusalem encircled, engirded, and surrounded by a defensive perimeter. It probably isn't a coincidence that the separation wall is built in largely the same place as the wall in the lower left quarter of the map above. Topography remains, even after time has swept away memory. The surface of the city itself seems to dictate the contours of its history.
And then there is this most venerated barrier in the world. Those who worship at the Western Wall believe that it is a barrier between man and God. The closest proximity to the divine which material existence can provide. Walls, after all, are only built because of their proximity to what is on the other side of them.
Paradoxically, a city which exists so infinitely in the mind may require physical barriers simply to keep itself even vaguely sane. Jerusalem is conceived of in the religious mind as a pale reflection of a heavenly Jerusalem. No city in the world -- even Rome -- has been so consistently transformed into transcendent metaphor, allegory, and dream. The city seems to respond by an equally consistent urge to demarcate itself, to physically limit its borders, as if, without them, it would simply fly off the face of the earth. In this sense, it may most precisely echo its identity as a Jewish city. Judaism is furiously demarcated on earth and infinitely unlimited in the mind. To a great extent, earthly Judaism exists in a series of opposites: Jew and Gentile, Shabbat and the work week, the holy and the profane, the Temple and everywhere else, the Holy of Holies and the Temple, the Tanach and every other book every written, etc. Spiritually, however, Judaism presents itself as essentially limitless. Interpretation of the holy texts, for instance, is accomplished according to a structure called Pardes, four levels of interpretation, each more esoteric than the other. Within each Pardes, however, is another Pardes, and so on and so forth, ad infinitum. The possibilities of interpretation and thus expansion are, theoretically at least, completely limitless. Jerusalem, I fear, suffers from a similar infinitude, and thus may require that, on earth at least, it remain firmly inside its walls.