A big part of the Celtic culture was based on the spiritual and supernatural scope. In fact, Celtic warriors tended to associate supernatural properties with many natural parameters, including bogs, rivers, lakes, mountains, and even trees.
The spiritual scope and its characteristics also extended to certain animals and birds, like horses, wild boars, dogs, and ravens. To that end, many of the Celts considered the tangible realm of man to be co-existing with the Otherworld where the gods and dead resided.
At times, the boundary between these two realms was judged to be ‘thinned’, and as such few of the human sacrifices (like the Lindow Man) were made to ‘send’ a messenger into this fantastical Otherworld.
The eminence of the Druids stemmed from their alleged capacity to ‘link’ and interpret the Otherworld. Their very name is derived from the cognate for oak trees; with the sacred grove of oak trees, known as drunemeton (in Galatia), being used for important rituals and ceremonies.
In that regard, while Druids were more popular in ancient Gaul and Britain, men with high social status who acted as the guardians of tribal traditions were common in the Celtic world (even in distant Galatia in Asia Minor).