Oldbury Castle hillfort, Cherhill Down, Wiltshire. Located on Cherhill Down, 5km west of Avebury, Oldbury castle hillfort is crowned by the Lansdowne obelisk, a conspicuous landmark in this part of north Wiltshire. The obelisk was erected in 1845 by Lord Lansdowne, ostensibly to commemorate his ancestor Sir William Petty, although it served equally well to proclaim how wealthy and powerful the family had become. The National Trust own the site, OLDBURY Castle is an irregularly shaped, well-defended iron age hill fort sited above Cherhill white horse, which is often known as the Oldbury White Horse. The hill fort encloses an area of about 25 acres (14.9 hectares) and has an entrance to the south-east. It is defended by sections of single and double rampart and ditch. During the 19th century excavations uncovered iron age pottery, and the site was subject to flint digging. ?005 Credit:TopFoto / Fortean