aerial photograph of Maesbury Castle small multivallate hillfort Somerset England UK. Maesbury Castle hillfort was constructed during the iron age and is typical of such structures. Most were built and occupied from around 600BC to 100 AD.Why so many hill forts were constructed during a relatively small period of history is unknown, however their appearance coincided with the adoption of iron and an increase in population. It may be that the pressures of an increasing population coupled with new weaponary resulted in conflict.