As the text says, the height and placement of the fountain has to do with organizing and surveying the street traffic and knowing all of what happens in the city - but it is also applicable on a larger scale. This preoccupation with the view from below of the unknown above, and the view from above of the ordinary below, is symbolic of humanity's obsession with needing to knowing everything and not being able to, of needing to know the purpose of life and finding every answer to every question. If one could only climb the obelisk (like a stairway to heaven), look around, and climb back down safely, they would theoretically be able to see more than anyone else ever had, they'd see miles ahead of where they are now, know all of the divine secrets that life has to offer and be able to live having finally satisfied such a common, yet intense, desire to know everything that was and is to come. They would truly know everything. But since no one could climb it (practicality and sacredness) no one could possibly know what the view looks like from so high up (which is probably for the best - that information is way to existential and massive to be able to just ~return~ to ones ordinary, everyday life - hence, maybe prophets?). The closest humanity (then) could get to such heights and divine status were popes, as they preached from their high up balcony to the masses; and the few prophets who wrote the sacred texts and received divine visions (from their Holy Hill?). The paramount power that popes and prophets have and have had on the masses is exhaustive and can be seen in the literal purpose and physicality of the fountain and the renovation of the Piazzo - to redirect and manage the flow of the traffic, to manipulate the movements of the masses. The fountain reflects this considerable power - it is a vessel which physically manipulates the flow of water and symbolically converges 4 rivers that would never otherwise touch - the converging of the 4 rivers are symbolic of the expansion of power and conquering of different lands - suggesting a universal element (in this case religion, or more literally water (devout religion as crucial to life as water?)) that can facilitate world-wide communion and order. In this way, the fountain is both physically and metaphorically symbolic of the power of the papacy to lead, convert and bring people together; it reflects both the common wo/man looking up at God and at those figures who represent His divinity and holiness and wondering what the view is like from up there - would knowing what is up there make life any easier? Would everything suddenly make sense?; it is symbolic of the vast power that the servants of God (popes and proceeding hierarchy; prophets) have to conform and mold the laity through sermon and a perceived (constructed?) holiness; symbolic in its physical manipulation of water and the traffic of the people who literally look up to and crane their necks to hear, or even catch a glimpse of the papacy, people who devoutly live by the bible so that, one day, they can climb to the top and see what He sees; symbolic of the obsession humanity has with deities and the power that that obsession holds over them; and, finally, symbolic of that ever-present desire to have all of the answer that are inaccessible (or don't exist).