Hillforts in Britain refers to the various hillforts within the island of Great Britain. Although the earliest such constructs fitting this description come from the Neolithic period, with a few also dating to the later Bronze Age, British hill forts were primarily constructed during the Iron Age. Some of these were apparently abandoned in the southern areas that were a part of Roman Britain, although at the same time, those areas of northern Britain that remained free from Roman occupation saw an increase in their construction. Some hillforts were reused in the Early Medieval period, and in some rarer cases, into the Later Medieval period as well. By the Early Modern period these had essentially all been abandoned, with many being excavated by archaeologists in the nineteenth century onward.
There are around 3,300 structures that can be classed as hillforts or similar "defended enclosures" within Britain. Most of these are clustered in certain regions: south and south-west England, the west coast of Wales and Scotland, the Welsh marches and the Scottish border hills. British hillforts varied in size, with the majority covering an area of less than 1 ha (3 acres), but with most others ranging from this up to around 12 ha (30 acres) in size. In certain rare cases, they were bigger, with a few examples being over 80 ha (200 acres) in size.
A hillfort or hill fort is a type of earthworks used as a fortified refuge or defended settlement, located to exploit a rise in elevation for defensive advantage. They are typically European and of the Bronze and Iron Ages. Some were used in the post-Roman period. The fortification usually follows the contours of a hill, consisting of one or more lines of earthworks, with stockades or defensive walls, and external ditches. Hill forts developed in the Late Bronze and Early Iron Age, roughly the start of the first millennium BC, and were in use in many Celtic areas of central and western Europe until the Roman conquest.
The terms "hill fort", "hill-fort" and "hillfort" are all used in the archaeological literature. They all refer to an elevated site with one or more ramparts made of earth, stone and/or wood, with an external ditch. Many small early hill forts were abandoned, with the larger ones being redeveloped at a later date. Some hill forts contain houses.
Similar but smaller and less defendable earthworks are found on the sides of hills. These are known as hill-slope enclosures and may have been animal pens.