I have been there years ago. There is another theory that these are Victorian fakes. They show little sign of habitation, eg remains of stuff or lost things. Which is also why dating them is hard.
Of course perhaps 2000 years ago people were bored and did it for fun too, it could still be historic.
https://www.theguardian.com/society/2006/aug/08/communities....
8 kilometer long tunnel, how the heck did you accurately connect it. They told the story but there was not much accuracy of where it was.
Baddies come, you hide in the ground, they light fires on top and kill you all or bury you etc. Being in a constrictive space with the enemy outside seemed a bad idea.
It's not like bunkers which are used against aerial bombings. Or escape tunnels to go from A to B.