In the immediate vicinity of the large Italian cathedrals / basilicas there is always a separate baptistery (which in important cities can sometimes take on the dimensions of a church), called a “baptistery”. Saint John the Baptist, like Saint Joseph, is a man on the threshold from the Old to the New Testament. His parents are Zacharias and Elisabeth. After the announcement of God's incarnation, the Mother of God visits her relative Elisabeth, who will give birth to a son in her old age, John the Baptist.
He is half a year older than Jesus and is considered his forerunner/pioneer. He lives in the desert, preaches repentance from sins to the Jewish population and baptizes them in the Jordan. Jesus also comes there to be baptized, and is filled with the Holy Spirit who descends on him from heaven.
John the Baptist's memorial day in the saints' calendar is on June 24th, exactly half a year before 'Holy Eve'.