During the Jubilee called by Pope Boniface VIII, a famous episode occurred, recalled by a man called Consiglio di Michele dei Cerchi in his book of Ricordanze [1] (i.e., Recollections).
Twelve Florentine ambassadors were sent in 1300 to Rome by Pope Boniface VIII, by prayed gentlemens and princes as will be said below, coming from many different nations. […] As said Pope Boniface went about the place of St. John with many cardinals and other company of prelates, he marveled at the great mangnificence of the city of Florence, and asking all the prelates what city Florence was, and why it was not inferior to any in particular, he asked it three times before it was answered, and not having been answered he became disturbed and said, “If you do not answer me I will have you put in the malta, that is a prison so called.” [Dante cites this prison in Paradiso IX, 52-54] Then the cardinal of Spain [perhaps Gonzalo Pérez Gudiel, though he died in 1299] not very benevolent with the Florentines replied, “Holy Father, Florence is a good city.” Hearing this the Pope said to him, “O Spanish mule (sic) have you no regard for twelve ambassadors who have been sent, among whom are princes and lords of Christendom and from the Great Tartar, who are all Florentines and govern our court? The Florentines even rule the world. The world is governed by four elements: air, fire and water and earth. I say that the Florentines are the fifth element and so I approve.” […].
The earliest evidence of this episode is found in a Laurentian Codex [2], written by Friar Tedaldo Della Casa between 1377 and 1383 and entrusted by him to the the Franciscan convent of Santa Croce. Although this version is referred to as that of Friar Tedaldo, it seems that it was not written by him. Anyway, recent studies reported in [1] discuss different accountings of the episode.
Sources:
[2] Biblioteca Medicea Laurenziana, Ms. Plut. XXVI, sin. VIII, Iste liber fuit ad usum Fratris Thebaldi De Casa quem vivens assignavit armaria fratrum (minor.) florentini conventus 1406.