There's nothing on the OS map about a well, and its not mentioned in the monument scheduling either. Are you sure you have got the right Caesar's Camp? - there are lots of hillforts with this name in the UK.
I think its likely that its this that you are looking for...
http://www.megalithic.co.uk/article.php?sid=10603
Hope this helps.
Something is not right. This message is just to keep things from messing up down the road