Caesar's invasions of Britain in the context of "Commentarii de Bello Gallico"

Gaius Julius Caesar (12 or 13 July 100 BC – 15 March 44 BC) was a Roman general and statesman. A member of the First Triumvirate, Caesar led the Roman armies in the Gallic Wars before defeating his political rival Pompey in a civil war. He subsequently became dictator from 49 BC until his assassination in 44 BC. Caesar played a critical role in the events that led to the demise of the Roman Republic and the rise of the Roman Empire.

In 60 BC, Caesar, Crassus, and Pompey formed the First Triumvirate, an informal political alliance that dominated Roman politics for several years. Their attempts to amass political power were opposed by many in the Senate, among them Cato the Younger with the private support of Cicero. Caesar rose to become one of the most powerful politicians in the Roman Republic through a string of military victories in the Gallic Wars, completed by 51 BC, which greatly extended Roman territory. During this time, he both invaded Britain and built a bridge across the river Rhine. These achievements and the support of his veteran army threatened to eclipse the standing of Pompey. The alliance between Caesar and Pompey slowly broke down and, by 50 BC, Pompey had realigned himself with the Senate. With his command expiring and the Gallic Wars largely concluded, the Senate ordered Caesar to step down from his military command and return to Rome. In early January 49 BC, Caesar openly defied the Senate by crossing the Rubicon and marching towards Rome at the head of an army. This began Caesar's civil war, which he won, leaving him in a position of near-unchallenged power and influence in 45 BC.

Historia regum Britanniae (The History of the Kings of Britain), originally called De gestis Britonum (On the Deeds of the Britons), is a fictitious account of British history, written around 1136 by Geoffrey of Monmouth. It chronicles the lives of the kings of the Britons over the course of two thousand years, beginning with the Trojans founding the British nation and continuing until the Anglo-Saxons assumed control of much of Britain around the 7th century. It is one of the central pieces of the Matter of Britain.

Although taken as historical truth until the 16th century, it is now considered to have no value as history. When events described, such as Julius Caesar's invasions of Britain, can be corroborated from contemporary histories, Geoffrey's account can be seen to be wildly inaccurate. It remains, however, a valuable piece of medieval literature, which contains the earliest known version of the story of King Lear and his three daughters, and helped popularise the legend of King Arthur.

The Welsh (Welsh: Cymry) are an ethnic group and nation native to Wales who share a common ancestry, history and culture. Wales is one of the four countries of the United Kingdom. The majority of people living in Wales are British citizens.

In Wales, the Welsh language (Welsh: Cymraeg) is protected by law. Welsh remains the predominant language in many parts of Wales, particularly in North Wales and parts of West Wales, though English is the predominant language in South Wales. The Welsh language is also taught in schools in Wales; and, even in regions of Wales in which Welsh people predominantly speak English on a daily basis, the Welsh language is spoken at home among family or in informal settings, with Welsh speakers often engaging in code-switching and translanguaging. In the English-speaking areas of Wales, many Welsh people are bilingually fluent or semi-fluent in the Welsh language or, to varying degrees, capable of speaking or understanding the language at limited or conversational proficiency levels. The Welsh language is descended from Brythonic, spoken across Britain since before the Roman invasion.

The Iceni (/aɪˈsiːnaɪ/ eye-SEEN-eye, Classical Latin: [ɪˈkeːniː]) or Eceni were an ancient tribe of eastern Britain during the Iron Age and early Roman era. Their territory included present-day Norfolk and parts of Suffolk and Cambridgeshire, and bordered the area of the Corieltauvi to the west, and the Catuvellauni and Trinovantes to the south. In the Roman period, their capital was Venta Icenorum at modern-day Caistor St Edmund.

Julius Caesar does not mention the Iceni in his account of his invasions of Britain in 55 and 54 BC, though they may be related to the Cenimagni, whom Caesar notes as living north of the River Thames at that time. The Iceni were a significant power in eastern Britain during Claudius' conquest of Britain in AD 43, following which they allied with Rome. Increasing Roman influence on their affairs led to revolt in AD 47, though they remained nominally independent under king Prasutagus until his death around AD 60. Roman encroachment after Prasutagus' death led his wife Boudica to launch a major revolt from 60–61. Boudica's uprising seriously endangered Roman rule in Britain and resulted in the burning of Londinium and other cities. The Romans finally crushed the rebellion, and the Iceni were increasingly incorporated into the Roman province.

The Roman client kingdoms in Britain were native tribes which chose to align themselves with the Roman Empire because they saw it as the best option for self-preservation or for protection from other hostile tribes. Alternatively, the Romans created (or enlisted) some client kingdoms when they felt influence without direct rule was desirable. Client kingdoms were ruled by client kings. In Latin these kings were referred to as rex sociusque et amicus, which translates to "king, ally, and friend". The type of relationships between client kingdoms and Rome was reliant on the individual circumstances in each kingdom.

The beginnings of the system are to be found in Caesar's re-enthroning of Mandubracius as king of the Trinovantes, who had been dethroned by Cassivellaunus and then aided Caesar's second invasion of Britain in 54 BC. The system further developed in the following hundred years, particularly under Augustus's influence, so that by the time of the Roman invasion in 43 AD several Roman client kingdoms had become established in the south of Britain. Client kingdoms were annexed when Rome needed to reaffirm their power in Britain or when the client kings could not manage the kingdoms and surrounding areas any more.

Cassivellaunus was a historical British military leader who led the defence against Julius Caesar's second expedition to Britain in 54 BC. He led an alliance of tribes against Roman forces, but eventually surrendered after his location was revealed to Julius Caesar by defeated Britons.

Cassivellaunus made an impact on the British consciousness. He appears in British legend as Cassibelanus, one of Geoffrey of Monmouth's kings of the Britons, and in the Mabinogi, Brut y Brenhinedd and the Welsh Triads as Caswallawn, son of Beli Mawr.