Baptistery of San Giovanni alle Fonti

This paleo-Christian baptistery (489–512 AD), commissioned under Bishop Laurentius, contained an octagonal font once lined with marble and mosaic. Located beneath Milan Cathedral, it served Ambrosian rites — the distinct Milanese form of Christian worship derived from St. Ambrose — until its burial and rediscovery in 1912. The structure marks a documented phase in Milan’s early Christian liturgy and architecture.