The Twin Apse Baptismal Hall
The First Archaeological Excavation
The 1958 excavations conducted by L. M. Belloni unearthed the building. Two distinct phases of construction were identified. Mario Mirabella Roberti analysed the Baptistery. Restoration works of the apse mosaics was started in 1960.
The first baptismal building probably dates to the fifth century. It was a single room (approximately 16×7 m) aligned East-West. The lateral walls converged into a single apse.
The floor of the apse was adorned with mosaics depicting marine scenes. Only one fish figure has survived. The nave was paved with cocciopesto (mortar mixed with powdered brick).
The baptismal font used for the immersion of adults was an octagonal pool built of bricks mixed with cocciopesto and clad with marble. The underlying rock, which prevented the construction of a water drainage system, is probably why the font had to be placed in an off-centre position. The two square rooms discovered under the church of St. John were probably associated with this building.
Two graves date to the same period. The first (an arcosolium) was placed in a niche hollowed out of the western wall of the apse, the second lies almost in the centre of the room. The construction of the twin apse hall dates to the Early Middle Ages. During this period the nave was paved with Moltrasio stone slabs; the mosaics of the two apses were relaid and the walls were frescoed with geometric designs that can be dated between the eighth and ninth centuries.
In 1169 the baptismal room and all the other buildings on the island were demolished.
Based on the archaeological data, the first construction phase has been ascribed to the Early Christian era (fifth century); the style of the mosaics and frescoes suggests that the building was converted to a twin apse hall during the eighth and ninth centuries.
In 2003 the Archaeological Heritage Office of Lombardy (Soprintendenza per i Beni Archeologici della Lombardia) has funded the restoration work of the baptismal hall. This consisted of the consolidation and cleaning of the frescoes and mosaics.