Although it's now the cathedral's baptistery, this wonderfully intact building was originally an ancient Roman temple dedicated to the king of the gods. It still has its original barrel-vaulted ceiling and decorative frieze, although a striking bronze statue of St John the Baptist by Ivan Meštrović now fills the spot where Jupiter once stood. The font is made from 13th-century carved stones recycled from the cathedral's rood screen.

　　Of the columns that once supported a porch, only one remains. The black-granite sphinx guarding the entrance was already ancient when the Romans dragged it from Egypt in the 3rd century. It was defaced (literally) by early Christians, who considered it a pagan icon.