The area has been occupied since the Paleolithic, with Mesolithic finds at Goldcliff and evidence of growing activity throughout the Bronze and Iron Age.
Gwent came into being after the Romans had left Britain, and was a successor state drawing on the culture of the pre-Roman Silures tribe and ultimately a large part of their Iron Age territories. It took its name from the civitas capital of Venta Silurum, perhaps meaning "Market of the Silures". In the post Roman period, the territory around Venta became the successor kingdom of Guenta, later Gwent, deriving its name directly from the town through the normal sound change in the Brythonic languages from v to gu. The town itself became Caerwent, "Fort Venta". Unlike in other Welsh territories, inhabitants of Caerwent and Caerleon retained the use of defensible Roman town walls throughout the period.
The medieval kingdom was traditionallySevern estuary. To the north, the area adjoined Ewyas and Ergyng (later known as "Archenfield"). According to one Old Welsh genealogy, the founder of the kingdom was Caradoc Freichfras. The earliest centre of the kingdom may have been at Caerwent, the Roman administrative centre, or perhaps Caerleon, formerly a major Roman military base. Welsh saints like Dubricius, Tatheus and Cadoc Christianized the area from the 5th century onwards. According to tradition, in about the 6th century Caradoc moved his court from Caerwent to Portskewett, perhaps meaning nearby Sudbrook. Other suggestions are that Gwent was founded by Erb, possibly a descendant of Caradoc, who may have been a ruler of Ergyng east of the Black Mountains who won control of a wider area to the south.
taken to be the area between the Usk, the Wye, and
A later monarch was the Christian King Tewdrig who was mortally wounded repelling a pagan Saxon invasion. His son Meurig may have been responsible for uniting Gwent with Glywysing to the west in the 7th century, through marriage. It has been suggested that Meurig's son, Athrwys, may be the origin for King Arthur, although others consider this unlikely.
At times in the 8th century, Gwent and Glywysing appear to have formed a single kingdom. Gwent may also have extended east of the River Wye into areas known as Cantref Coch, which later became the Forest of Dean. Its eastern boundary later became established as the Wye, perhaps first determined by Offa of Mercia's dyke in the late 8th century, and certainly by Athelstan of England in 927. The area west of the River Usk was Gwynllŵg, which formed part of Glywysing.
In 931, Morgan ab Owain of Gwent, later known as Morgan Hen (Morgan the Old), was one of the Welsh rulers who submitted to Athelstan's overlordship, and attended him at court in Hereford. However, Gwent remained a distinct Welsh kingdom. In about 942, Gwent and Glywysing were again temporarily united under the name of Morgannŵg by Morgan Hen, but they were broken up again after his death. In 1034 Gwent was invaded by Canute.
Gwent's existence as a separate kingdom again temporarily ended when Gruffydd ap Llywelyn won control of the area and Morgannŵg in 1055, so extending his rule over the whole of Wales. In 1056 Gruffyd ap Llywelyn campaigned from the vicinity of Monmouth with an army of Welsh, Saxons and Danes to defeat Ralph, Earl of Hereford, ravaging the surrounding countryside. However, after Gruffydd's death in 1063, Caradog ap Gruffudd re-established an independent kingdom in Gwent under his father's 2nd cousin Cadwgan ap Meurig. In 1065 the area was invaded by Earl Harold of Hereford, who attempted to establish a base at Portskewett, but it was razed to the ground by Caradog, and Harold - having by then been crowned King of England - was killed at the Battle of Hastings the following year.
With the Norman invasion of Britain, the Normans sacked south-east Wales and parts of Gwent in response to Eadric's Herefordshire rebellion in alliance with the Welsh prince of Gwynedd (and Powys), Bleddyn ap Cynfyn. King Maredudd of Deheubarth decided not to resist the Norman encroachment on Gwent and was rewarded with lands in England in 1070, at the same time as the chronicler Orderic Vitalis noted in his Historia Ecclesiastica that a Welsh king named "Caducan" (Cadwgan ap Meurig) suffered defeat in battle at the hands of William FitzOsbern, 1st Earl of Hereford. With the Norman invasion of Wales extending westwards, Caradog's area of control moved into Deheubarth to the west, and in 1074 Caradog took over control over what was left of the war-ravaged Kingdom from Cadwgan ap Meurig.
By Caradog's death in 1081 most of Gwent had become firmly under Norman control. The Normans divided the area, including those areas which they controlled beyond the River Usk, into the Marcher Lordships of Abergavenny, Caerleon, Monmouth, Striguil (Chepstow) and Usk. Welsh law as seen through Norman eyes continued, with Marcher lords ruling sicut regale ("like a king") as stated by Gilbert, Earl of Gloucester.
The Normans lords freely built permanent stone castles, many originating from a network of earlier motte and bailey castles. The density of castles of this type and age is amongst the highest in Britain and certainly the rest of the Welsh Marches, with at least 25 castle sites remaining in Monmouthshire alone today.
Conflict with the Welsh continued intermittently, although the Welsh Lord of Caerleon, Morgan ab Owain, grandson of King Caradog ap Gruffudd, was recognized by Henry II c. 1155, with Caerleon remaining, in welsh hands, subject to occasional struggles, until William Marshal retook the castle in 1217 from Morgan ap Hywel.