I just returned from a hiking trip in the Vosges mountains in Alsace, France. We visited several castles and ruined castles that were placed on mountain tops an hour or more hike from the nearest village. Was this a common occurrence in France and the rest of Europe during the medieval period ? How was a castle that far away helpful? Thank you.
In Britain in particular before the Norman conquest towns were the primary focus of fortification. These Burghs (from which we get the word 'borough') consisted of walled fortifications around towns to protect those within. The Normans largely abandoned this idea in favour of building what we identify as Castles which were used as a method to control an often rebellious population and subdue rival forces. This approach was largely followed thereafter.
As far as I understand it in the early medieval period, the Dark Ages if you will, there was a much more amicable relationship between the population and the ruling elite. Fortified towns were there to keep out foreign invaders and undesirables on behalf of all. Later when the Kings etc were not so popular they were the ones building the castles to help defeat and control their rivals, be they pesky locals or foreign rulers and their armies.
That isn't necessarily common. Frequently villages would be built around and expand outward from the castles. Most of the villages you see today are actually more recently constructed, even if the houses are over a hundred years old. That isn't to say some castles wouldn't be constructed away from the village, if some terrain feature could be exploited. Castles fell out of vogue once gunpowder artillery really caught on in the 16th century, and consequently gave rise to the 'star fort'.