As early as the 2nd century AD, infant baptism had begun to gain acceptance among Christians for the spiritual purification and social initiation of infants. The requirement for some confession of faith necessitated the use of adults who acted as sponsors for the child. They vocalized the confession of faith and acted as guarantors of the child’s spiritual upbringing.
Normally, these sponsors were the natural parents of a child, as emphasized in 408 by St. Augustine who suggested that they could, it seems exceptionally, be other individuals. Within a century, the Corpus Juris Civilis indicates that parents had been replaced in this role almost completely. This was clarified in 813 when the Council of Munich prohibited natural parents from acting as godparents to their own children.
By the 5th century, male sponsors were referred to as "spiritual fathers", and by the end of the 6th century, they were being noted to as "compaters" and "commaters", suggesting that these were being seen as spiritual co-parents. This pattern was marked by the creation of legal barriers to marriage that paralleled those for other forms of kin. A decree of Justinian, dated to 530, outlawed marriage between a godfather and his goddaughter, and these barriers continued to multiply until the 11th century, forbidding marriage between natural and spiritual parents, or those directly related to them. As confirmation emerged as a separate rite from baptism from the 8th century, a second set of sponsors, with similar prohibitions, also emerged. The exact extent of these spiritual relationships as a bar to marriage in Catholicism was unclear until the Council of Trent, which limited it to relationships between the godparents, the child, and the parents.
Luther, Zwingli, and Calvin preserved infant baptism against the attacks of more radical reformers including Anabaptists, and with it, sponsors at baptism. However, Luther strongly objected to the marriage barriers it created, Zwingli stressed the role of parents and pastors, rather than the "witnesses", in religious instruction, and Calvin and his followers tended to prefer the sponsors to be the natural parents. A single godparent was retained in baptism at Geneva and among French Calvinists, but some followers of Calvin, most notably in Scotland and eventually the English colonies in America, rejected them altogether.
In the early church, one sponsor seems to have been the norm, but in the early Middle Ages, there seems to have been two, one of each sex, and this practice has been largely maintained in Orthodox Christianity. In 888, the Catholic Council of Metz attempted to limit the number to one, but proliferation seems to have continued. In early 14th-century Spain, as many as 20 godparents were being chosen. In England, the Synod of Worcester (1240) stipulated three sponsors (two of the same sex and one of the opposite), and this has remained the norm in the Church of England. The Council of Trent attempted to limit the numbers of godparents to one or two, but practice has differed across the Catholic world.