abandoned; the folk disperse quietly soon after noon, when business is done, leaving Yarnbury to the silent occupation of its prehistoric ghosts for another year. Ecology Yarnbury Castle is located in an area of unimproved grassland on the upper chalk north of the Wylye Valley, and on the edge of Salisbury Plain, which is the largest remaining area of calcareous grassland in north-west Europe. The local area supports a rich and diverse grassland flora, which led to it being declared a biological Site of Special Scientific Interest in 1951. Designated as Yarnbury Castle SSSI, the site encompasses a total of . The SSSI designation for the site arises due to interest in the biodiversity and species present upon the earthworks of the fort themselves, with the inner and surrounding parts of the site being of improved agricultural grassland of little interest. The earthworks support a rich chalk grassland flora, including several rare species. There are 16 species of grass and sedge recorded, among them upright brome (Bromus erectus), sheep's fescue (Festuca ovina), quaking grass (Briza media), crested hair-grass (Koeleria cristata), and dwarf sedge (Carex humilis). Various herb species include dwarf thistle (Cirsium acaule), chalk milkwort (Polygala calcarea), horseshoe vetch (Hippocrepis comosa), common thyme (Thymus praecox), squinancywort (Asperula cynanchica) and common rock-rose (Helianthemum nummularium). Rarer national species include field fleawort (Senecio integrifolius), bastard toadflax (Thesium humifusum), and burnt orchid (Orchis ustulata), fragrant orchid (Gymnadenia conopsea), and other orchids. The site was previously populated with scattered juniper (Juniperus communis) bushes, but these were removed and the current grazing regime ensures that they do not return. There are some invertebrates recorded, including marsh fritillary (Euphydryas aurinia) and small heath (Coenonympha pamphilus) butterflies, and a number of downland birds are present including the skylark, corn bunting and grey partridge. See also List of hillforts in England References Iron Age sites in England Buildings and structures in Wiltshire Hill forts in Wiltshire Archaeological sites in Wiltshire Scheduled monuments in Wiltshire Sites of Special Scientific Interest in Wiltshire Sites of Special Scientific Interest notified in 1951 Hills of Wiltshire