There can be no doubt that the cognomen Paullus, or Paulus, the contraction of pauxillus, originated with one of the Æmilian gens, who was small in stature.  It was common in other gentes, though chiefly distinguished among the Æmilii, and was most probably the name by which "Saul of Tarsus" would have been enrolled as a citizen, either from its resemblance to his Jewish name, or from the person who had conferred liberty upon his parents.  Some, however, imagine that he assumed it out of compliment to the deputy, Sergius Paulus; others, that it was an allusion to his "weakness" or "bodily presence," or that he took it in his humility, meaning that he was "less than the least of the Apostles."  Be that as it may, he has given it an honour entirely outshining that which is won from the Æmilii, and has spread Paul throughout Europe. (History of Christian Names, Yonge, 1884)