Before Christianity was approved under Constantine, baptism took place where there was flowing water, such as waterfalls. When buildings were allowed, a tradition developed in Italy that baptisteries should be separate buildings, usually next to a cathedral. Baptisms in medieval times only took place two or three times a year, and were performed by the bishop, which explains their large size and location. Early baptisteries were designed for total immersion, which explains the large size of many of the fonts. Italian churches described as a ‘pieve’ also undertook baptism, usually because the cathedral of the diocese was a long distance away.
  The shape of the baptistries reflects Roman mausoleums. Baptism, like death, was seen as an important moment of transition. Many are octagonal, which is said to refer to the eight days between the crucifixion and Christ's appearance to the apostles: a symbol of resurrection. An alternative and perhaps more convincing reading is that there were six days of creation, and God rested on the seventh day. The eighth day could refer to a new creation, a new beginning, a resurrection.
  Click on the photographs to read about the baptisteries: more to come! I have already written about the baptistery of Pisa and the two baptisteries in Ravenna: the link takes you there.