An important source has always been the names of famous saints. The church strongly encouraged the giving of saintly names to children, and this encouragement continues in Catholic countries. Some of these saints appear in the New Testament, while others play roles in later history and legends. Old Testament names were not commonly used by Christians until relatively recent times.
Roman names were spread by the far-reaching Roman Empire.
Germanic names spread with the Germanic tribes from their original homes in northern Europe. During the first millennium a great deal of the continent came under Germanic rule and thus their names were imported into southern regions such as Spain and Italy.
Slavic names are used in several countries of eastern and central Europe.
Celtic names are mostly confined to the British Isles and the English-speaking world.