<P> The boundaries of Salisbury Plain have never been truly defined, and there is some difference of opinion as to its exact area . The river valleys surrounding it, and other downs and plains beyond them loosely define its boundaries . To the north the scarp of the downs overlooks the Vale of Pewsey, and to the north west the Bristol Avon . The River Wylye runs along the south west, and the Bourne runs to the east . The Hampshire Avon runs through the eastern half of the plain and to the south the plain peters out as the river valleys close together before meeting at Salisbury . From here the Avon continues south to the English Channel at Christchurch . The Hampshire Downs and the Berkshire Downs are chalk downland to the east and north of Salisbury Plain, and the Dorset Downs is to the south west . In the west and north west the geology is mainly of the clays and limestones of the Blackmore Vale, Avon Vale and Vale of Wardour . </P> <P> Amesbury is considered the largest settlement on the plain, though there are a number of small villages, such as Tilshead, Chitterne and Shrewton in the middle of the plain, as well as various hamlets and army camps . The A303 road runs along the southern area of the plain, while the A345 and the A360 cut across the centre . </P> <P> Salisbury Plain is famous for its history and archaeology . In the Neolithic period Stone Age man began to settle on the plain, most likely centred around the causewayed enclosure of Robin Hood's Ball . Large long barrows like White Barrow and other earthworks were built across the plain . By 2500 BC areas around Durrington Walls and Stonehenge had become a focus for building, and the southern part of the plain continued to be settled into the Bronze Age . </P> <P> Around 600 BC Iron Age Hill forts came to be constructed around the boundaries of the plain, including Scratchbury Camp and Battlesbury Camp to the south west, Bratton Camp to the north west, Casterley Camp to the north, Yarnbury and Vespasian's Camp to the south, and Sidbury Hill to the east . </P>

Famous circular landmarks located on the salisbury plain of england