As the name suggests, there was once a castle at the top; a mediaeval castle that lasted maybe 200 years. But is everything as it might seem to be ?
It appears that the sides of the hill have been artificially steepened, and it's generally supposed this was done for defensive reasons, etc. But when ? ...Was it in mediaeval times ? ...Or could it possibly have been carried out, perhaps for other reasons, in the megalithic period, say 5000 years ago ? ...In this respect, it might not be unreasonable to compare it in some ways with other unusual hills in Britain, perhaps even in one or two respects with Silbury Hill in Wiltshire.
Whatever the situation, it remains the case that Castle Hill is a mystery, and that only a limited amount is known about the castle that once stood on its flattened apex. It's widely believed that stones from the castle were used when building some of the houses in Mere, yet even here there is much evidence to be collected.