Forgive me, because I know little about how these types of things are determined, but I'm curious how anthropologists/archaeologists/etc. arrive at these types of conclusions. Is there evidence of a cult that existed around that time that thought this way, or is this just an educated guess based upon society at the time?
The default explanation for everything (coffee makers, toilet seats, etc) was that it served some religious purpose, because if you can't figure out a useful purpose for some object, "religious relic" can pretty much fit anything.
- entrances are generally hidden
- narrow slip holes make defense simple
- locking mechanisms that can only be operated from the inside were found
- some are directly connected to fortifications
But it would also be excessively easy for an attacker to just kill the inhabitants by sealing the entry / smoking them out if they were found. They're also rather unsuitable for prolonged hiding (little space = little air, need to bring food, no way of getting rid of faeces other than burying them), but 48h have been experimentally confirmed as possible for 3 adults.
One piece of evidence that comes to mind is recorded before the Stellinga uprising in the 9th century. Lothair, in his rebellion, got support of the local Stellinga (of doubtful religious allegiance) by promising them "if they should side with him, that he would let them have the same law in the future which their ancestors had observed when they were still worshiping idols." (From Scholz's Carolingian Chronicles, translations of Nithard's Histories).
Unfortunately, hints such as this are few and far between, but it still supports the idea that older cults may have been enduring. And of course, the last sentence about slipping off diseases, guilts and rebirth... that's just the little Wikipedia touch.
They are all around my home village.
The historian Cassius Dio wrote "[The Jews] did not dare try conclusions with the Romans in the open field, but they occupied the advantageous positions in the country and strengthened them with mines and walls, in order that they might have places of refuge whenever they should be hard pressed, and might meet togethere unobserved under ground; and they pierced these subterranean passages from above at intervals to let in air and light".
yellow: shaft used during construction, later filled up