Much ink has been shed explicating the figure, who draws on Classical images of Hercules. In the context though, it is surely a Celtic fertility god.
Well, no. Scholar Ronald Hutton points out that the figure is not even referred to before the late 17th century, unlike other authentic monuments like Stonehenge, which had intrigued travelers through the Middle Ages. By far the most likely conclusion is that this impressive figure, with his giant phallus and club, is meant to depict not Hercules but... Oliver Cromwell. The local landowner in the 1650s was a Royalist Anglican who loathed Cromwell's Puritan regime. In internal exile on his estate, he whiled away his time ordering the construction of a savage chalk-cut cartoon of the dictator, with the large club indicating the regime's total lack of legitimacy.
Cerne Abbas isn't a pagan idol, it's a dirty joke.
No I won't paste a picture...this is a PG rated blog.
more on dating problems here.
these figures would disappear if not continually dug out, making dating more complicated. So the giant might have been there but not very easy to see, but was changed to ridicule Cromwell.
The link also has an article on identifying ancient disease by DNA sampling.