The new baptistery behind the tower on the east side of the church was built in the middle of the 17th century. It replaced its predecessor, a similar central eight-sided building that stood on the other side of the church in the 16th century. The building in Piran is the only preserved baptistery with its foundational purpose in Slovenia. The Baroque building is accented by the decorative, blank lantern on the roof. The entrance into the baptistery is elevated above the platform and double staircase. The interior area is a central octagon. On the north side it has a smaller presbytery added on. The baptistery in the middle of the octagon was remade from the Roman stone product with a relief of a dolphin and is probably the oldest monument of Piran. On the wall hangs an exceptional Early Gothic ramified cross with a statue of Christ (Venetian workshop, 1310). Numerous paintings depict the stations of Mary's life (16th and 17th centuries). Rarities are the built in plates with woven ornaments (9th-11th centuries). The keys of the baptistery are kept in the vicarage.