In AD 753, Pope Stephen was driven from Rome by Adolphus, King of the Lombards. He fled to Pipen. While he was there, he was asked by the monks of Cressy, in Brittany, if, in the case of necessity, baptism poured on the head would be lawful, in place of immersion. This was 723 years after the beginning of Christian baptism in AD 30 (Acts 2:38). Even then, it was allowed only in the case of extreme emergency. The common practice remained immersion.
In 1311 AD, the Counsel of Ravenna declared sprinkling or immersion to be valid. There was no claim that sprinkling was scriptural. The change was made by a majority vote of the College of Cardinals. It was the product of the superstitious theology of the Middle Ages which had long since lost sight of the Biblical reasons for baptism.
--P.H. Welshimer "Why I Did Not Baptize The Baby"