Rectangular white marble plaque, datable to the second half of the 13th century, coming from an unspecified place inside the Baptistery, bearing an inscription in Latin engraved across the field, which reads:

“You have been baptized, anointed with chrism, purified with hyssop, you have been reborn at the living springs

Strengthen your hearts so that your faith may grow: fear God and always abide in him.

Those who crossed the sea came from Egypt, knew the divine power and sang its praises. Glory to you, O Christ, gracious reign; have mercy on us, you who died for us. And you, Giordano, why are you going back?”

The inscription is taken from an ancient baptismal hymn and therefore refers to the sacrament administered here: the Hyssop plant, mentioned several times in the Bible, is a plant that had the meaning of purification and ritual use therefore pertaining to baptismal water (cf Psalm 51:7: "Cleanse me with hyssop, and I will be clean; wash me, and I will be whiter than snow"). The salvific value of the water of Baptism is the reference to the passage of the Red Sea of ​​the chosen people fleeing Egypt (Book of Exodus, 13,17-14, 29). The last verse contains the Psalm where the Jordan River is mentioned, where in the New Testament Saint John, patron saint of the Baptistery and of Florence, baptized Christ.