The mythology of the ancient Basques largely did not survive the arrival of Christianity in the Basque Country between the 4th and 12th century AD. Most of what is known about elements of this original belief system is based on the analysis of legends, the study of place names and scant historical references to pagan rituals practised by the Basques.
One main figure of this belief system was the female character of Mari. According to legends collected in the area of Ataun, the other main figure was her consort Sugaar. However, due to the scarcity of the material it is difficult to say if this would have been the "central pair" of the Basque pantheon. Based on the attributes ascribed to these mythological creatures, this would be considered a chthonic religion as all its characters dwell on earth or below it, with the sky seen mostly as an empty corridor through which the divinities pass.
The Christianization of the Basque Country has been the topic of some discussion. Broadly speaking there are two views: either Christianity arrived in the Basque Country during the 4th and 5th century, or this did not occur until the 12th and 13th century. The main issue lies in the different interpretations of what is considered Christianization. Early traces of Christianity can be found in the major urban areas from the 4th century onwards, a bishopric from 589 in Pamplona and three hermit cave concentrations (two in Álava, one in Navarre) were in use from the 6th century onwards. In this sense, Christianity arrived "early".
At the same time, various historical sources and research directly or indirectly bear witness to the fact that large-scale conversion did not begin to take place until the 10th and 11th century:
Most Vasconists broadly agree that Christianity thus arrived some time in the 4th/5th century. Serious missionary and religious activity only began in the 9th century from the kingdom of Asturias and Franks, and continued after the Reconquista with famous monastic foundations (Monastery of Leyre, San Millán de la Cogolla) and the diocese of Bayonne in the 11th century. Thus Christian and non-Christian beliefs lived side by side past the 10th and 11th century. Various traditions connected to this ancient belief system have survived partly by adapting a Christian veneer or by turning into folk traditions, as happened elsewhere in Europe.