The Anglo-Saxons took a long time to arrive in Somerset after their first invasions of eastern Britain in the 5th century, but when they came, in AD 658, they were the first to give Somerset an identity. The Old English name for Somerset was Sumersaeton which came from the village of Somerton, meaning "farmstead used in summer" and the suffix saete, meaning "house". The word settler has a similar route. It was not until the Norman Conquest, after 1066, however, that Somerset became the name for the whole shire.

Somerset has a prehistory going back at least as far as 11,000 bc when families lived in Gough's Cave, near Cheddar, and hunted for food in the Cheddar Gorge. In about 4,300 bc, wooden causeways were built across the marshes. Somerset was only lightly populated then, but over the centuries, as more and more newcomers settled, it became a dangerous place where defence against attack was imperative. Great Iron Age hillforts were built, like Cadbury Castle, around 700 bc; but even these could not withstand the might of Rome.

The most notable of Somerset towns during Roman Times was of course, Bath. It was known to the Romans as Aquae Sulis or the Waters of Sulis, a Celtic goddess identified with wise Minerva. A huge classical temple dedicated to this lady started life here in the late 1st century, probably taking the place of a previous Iron Age establishment. It adjoined a vast baths complex, powered by the miraculous hot spring which still gushes forth today at a constant temperature of 46½ºC. It was one of the major religious curative centres in the whole of the Western Empire and pilgrims flocked there from across the known World. Despite the place's importance and the large scale excavations of the religious complex, relatively little is known of the town as a whole. It is thought that the later medieval city walls sit upon a Roman base, but these encompass only 25 acres: much smaller than most Romano-British towns. It has been suggested that these were temenos walls around the religious precinct and associated hostelries, rather than town-walls as such. Certainly there was further extensive urban areas around Walcot to the north of these walls.