The Borgia are the Spanish house about to take Rome, in the Invisible Cities chronicle (1494).
The warning from the heavens already names it: a Spanish cardinal, a certain Rodrigo, preparing the moves to ascend to the papal throne. He belongs to an important family, was sponsored by the first of the terrible popes, a certain Sixtus (Sixto), and now has good chances of being the next Pope. From the next generation, César Borgia emerges.
Position on Savonarola
In the division of factions over Savonarola, the Borgia hold the simplest position. Rome (the dukes of Romagna, the cardinals, the Borgia, the Pazzi) simply wants to assassinate him and hires the best weapons for it. Milan, represented by the Sforza, wants to control him; Florence is torn between wanting him and fearing him.