The first thing that will strike you with The Fountain of Tureen is the difference between the usual "beautiful white marble" used for the pool and the everyday travertine stone of the cover, which is hardly characteristic of Jacopo, who normally used travertine for his steps. However, there is something far more important: if you look very hard indeed you will see, carved in tiny letters on the middle collar beneath the knob on top of the lid of the fountain, the following proverb, as facile as it is philosophical: "Love God without fail. Do good and let others do the talking. MDCXXII". The date, 1622, is most important.

In a manuscript now in the Vatican Library, Theodor Ameyden wrote: "The 4th fountain for the Aqua Vergine is in Campo di Fiore, dressed with four bronze dolphins in a large marble shell". Theodor Sprenger provides a similar description (in Latin) of the same fountain: "Nor is the basin of the fountain in Campo di Flora, decorated with four bronze dolphins, unworthy of note". Finally, and perhaps more important as well as earlier than the last two documents, there is a large and very well known plan of Rome at the time of pope Paul V (1605-21).

This is the detailed map by Maggi, which shows the fountain in Campo dei Fiori, clearly still without a cover, as well as the ornaments around its sides which - though slightly less distinct - can nonetheless be recognised as the four dolphins mentioned by Ameyden and Sprenger. The same map also clearly shows that the "hollow" around the basin of the fountain was not rectangular as it was later and still is today but reproduced exactly the elongated form of the pool, which at that time had two short flights of steps at two opposite corners to allow access to the water spouts.