A few metres from the famous Porta del Paradiso, and ignored by almost everyone, stand two ancient porphyry columns.
The columns were a gift (1107) from the city of Pisa, in thanks for the aid Florence had provided in a naval battle against Muslim pirates in the Mediterranean sea.
The two columns were reputed to possess magical properties, as it was possible to see, reflected in their polished surface, any acts of treason against the state. However, the wily Pisans, before handing the columns over to the Florentines, passed them through a furnace, thus destroying their lustre and, consequently, their magical powers.
The two columns were once freestanding in the space between the Baptistery and the Cathedral, which was known as the paradiso, hence the nickname of Ghiberti's bronze door.