A: Reims, Grand Est, France
On Christmas Day, 496 Clovis I, king of the Franks, converted to Catholicism at the instigation of his wife, Clotilde, a Burgundian princess who was a Catholic in spite of the Arianism that surrounded her at court. Clovis was baptized in a small church in the vicinity of the subsequent Abbey of Saint-Remi in Reims.
"The followers of Catholicism believe that God, Jesus and the Holy Spirit are three persons of one being (consubstantiality), as opposed to Arian Christianity, whose followers believed that Jesus, as a distinct and separate being, was both subordinate to and created by God. While the theology of the Arians was declared a heresy at the First Council of Nicea in 325 AD, the missionary work of the bishop Ulfilas converted the pagan Goths to Arian Christianity in the 4th century. By the time of the ascension of Clovis, Gothic Arians dominated Christian Gaul, and Catholics were the minority. The king's Catholic baptism was of immense importance in the subsequent history of Western and Central Europe in general, for Clovis expanded his dominion over almost all of Gaul.
"... His [Clovis's] conversion to the Roman Catholic form of Christianity served to set him apart from the other Germanic kings of his time, such as those of the Visigoths and the Vandals, who had converted from pagan beliefs to Arian Christianity. His embrace of the Roman Catholic faith may have also gained him the support of the Catholic Gallo-Roman aristocracy in his later campaign against the Visigoths, which drove them from southern Gaul in 507 and resulted in a great many of his people converting to Catholicism...." (Wikipedia article on Clovis I, accessed 12-29-2013).