Must say I've felt for a long time now that hill forts had a dual purpose... the way many a Neolithic and Brionze Age monument were incorporated within sometimes quite cramped living space suggests to me that there was an 'other dimensional' aspect to hill forts; a combination of actual military power to metaphysical power. The siting of many, too - http://www.themodernantiquarian.com/site/8617/chesters.html is perhaps the most blatant example I've seen - also suggests there was a major aspect of 'bling' in the mix as well. Let's see how many banks and gateways we can have to get the message across to other tribes 'you don't even want to think about it'. So military (most certainly), ritualistic (seems that way to me) and sheer showing off.