Ancient historians managed to change the date of when the oil began to flow over the years, until the date became the very night that Christ was born. This was supposedly the very spot that the church of Santa Maria in Trastevere fountain would be built. The interpretations became so exaggerated that the last word is left to an anonymous writer who states: "In the Taberna Meritoria, on the spot with those two little iron-barred windows near the choir, at the time when our Lord Jesus Christ deigned to be born of the Holy Virgin, a most abundant fount of oil issued forth miraculously from the ground and for the space of a day and a night flowed in a wide stream down into the Tiber".
So what is the truth? A few years ago, an archeologist, had come to the conclusion, through excavation that there was petroleum in the area, making the theory of the oil well fountain theoretically possible.
The Latin author, Frontino, was a “Curator Aquarum” or Director for Water. This meant he was a very knowledgeable and reliable source on the aqueducts, fountains, and water courses.
Fontino was confused and puzzled as to why Augustus would send unhealthy, polluted water to the fountain since it came from the lake. He confirmed the water supplied to the Trastevere fountains was the same water from the Aqua Alsietina, possibly still in 1544.