The baptistery, due to its fame, has invariably attracted distinguished international visitors, including Luigi Vanvitelli in 1758, Hans Christian Andersen in 1834 (who also painted a portrait of the monument), King Ferdinand II in 1858, and King Gustav VI Adolf of Sweden and his wife in 1964.

Many of the visitors have created interesting depictions of the monument, which have been invaluable to scholars in outlining important phases of the monument’s history.