Geography of Dorset is the Blackmore Vale, a relatively low-lying area of clays and limestones of Jurassic age. The south-east of the county forms part of the Hampshire Basin, an asymmetric syncline covered in sands and gravels of Paleogene age. The main rivers in the county are the Stour, Frome and Piddle. The Stour is the county's largest river, although its source is in the neighbouring county of Wiltshire. The Frome and Piddle both lie wholly within the county. The whole of Dorset's coastline is designated part of the Jurassic Coast World Heritage Site, and contains examples of many different coastal landforms, reflecting
History of Dorset Dorset for 200 years after the withdrawal of the Roman legions. The inhospitable coastline prevented an invasion from the sea. When the Roman road across Cranborne Chase was rebuilt in the 6th century the Saxons advanced into Dorset. The Romano-British retreated, constructing another defence, Combs Ditch, which also fell within a century. It is thought that the Saxons captured east Dorset in the mid-7th century and west Dorset shortly afterwards, but the details are not known. Dorset was initially part of Saxon Wessex, with the first record of Dorset being in 841. Coenred, the sub-king of Dorset at the end