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The large, sixth-century octagonal basin complete with drain (right) was discovered to the east of the cathedral in 1866 and is protected to this day by a brick vault constructed by the cathedral’s head architect, Richard Voigtel. The basin was used for the Christian rite of baptism and bears all the hallmarks of such a sixth-century structure (e.g. the accentuated areas at the corners for the supports of a ciborium). It was built on top of the walls of a Roman house that already contained an octagonal basin. The floor at the bottom edge of the photo belonged to this Roman basin. Because the remaining wallsboth those of the house and those of the baptisterywere excavated and unfortunately almost completely destroyed long before the start of archaeological excavations, it is very hard to reconstruct the various different construction phases.
Sixth century: the large octagonal baptismal font with its original drain (right) was found in the eastern section of the cathedral in 1866 and protected until today by a brick vault built by the then Cathedral architect Voigtel. The Christian basin with forms characteristic of the sixth century (in case the marked corner foundations for the bases of the colums of the ciborium), was placed above the walls of a Roman house in which there also was an eight-sided basin. To this also belonged the seamless floor in the lower edge of the picture. Because the remaining walls, those of the house as well as the baptistery, were already covered a long time before archaeological excavation and unfortunately mostly destroyed, for this reason the reconstruction of the different points from the building phases are unclear.
In the foundation section of the baptismal pool there is below to the right a drainage outlet. On the exterior there is a rectangular opening which is visible on the inside with a lead pipe; this was connected to a channel which is now lost. The supply of baptismal water might have come from a stream above the basin edge located in the back to the left. (SR)
The around two meter pool on the inside has been dressed with waterproof mortar. To the right and left are the stairs for the baptismal candidates. The original top edge was probably a bit higher. The inner water-level reached about 0.5 meters, which is indicated by the height of the plastered walls. A person would have stood in the pool and baptized by poured water. In order to support the weight of the water as well as the basin and the ciborium to be reconstructed above the piscina, a strong foundation was required, here recognized above the older Roman phases. Above the top edge the drain was the floor of the baptistery whose upper sections were disguised. (SR)