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John Deare's Relief of Caesar's Invasion
John Deare's Relief of Caesar's Invasion

Julius Caesar's Invasion of Britain

Key facts about Julius Caesar's invasion of Britain

  • Caesar invaded Britain in 55 BCE'Before common era', the non-religious way of saying 'BC' (which means 'before Christ'). and 54 BCE
  • He invaded to stop Britons supporting GaulAn ancient region covering much of western Europe, including France, Belgium, Luxembourg, and parts of Switzerland, the Netherlands, Germany and northern Italy. during the Gallic Wars, and to enhance his own reputation.
  • His invasion was technically illegal, but the Senate granted him 20 days of thanksgiving
  • His 55 BCE invasion failed due to bad weather and sea conditions
  • In 54 BCE, Caesar was better prepared and managed to cross the River Thames
  • Caesar's invasion brought Britain to the attention of Rome

 People you need to know

  • Alexander the Great - king Alexander III of Macedon, who lived from 356 BCE until 323 BCE and created one of the largest empires of the ancient world.
  • Julius Caesar - famous Roman popularisLatin for 'favouring the people'. A popularis (plural populares) was a Roman politician in the Late Republic who derived power and support from the Roman masses. politician and general, who some feared wanted to be king.
  • Cassivellaunus - a British tribal chief who ruled over land north of the River Thames, probably belonging to the CatuvellauniA British Iron Age tribe in south-eastern Britain, with lands north of the Thames. tribe.
  • Mandubracius - king of the TrinovantesA British Iron Age tribe in south-eastern Britain, with lands on the north side of the Thames estuary covering modern Essex and Suffolk. tribe of south-eastern Britain.

Britain at the time of Caesar's invasion

During the Iron AgeThe Iron Age of the British Isles covers the period from about 800BCE to the Roman invasion of 43CE, and follows on from the Bronze Age. Britain was not a single nation but a collection of tribes, perhaps sharing a common language, but with differences in culture and belief. The area inhabited by each tribe shifted over time as political alliances changed and boundaries were disputed, with tribes appearing and disappearing as a result. Although the tribes have been described as warlike, they were also strong traders, both within the island and with the Continent, and there is evidence showing trade links between Britain and Europe since the Bronze AgeThe Bronze Age was a time between the Neolithic and the Iron Age, which is characterised by the use of the alloy bronze. In Britain it lasted from about 2500BCE until about 800BCE.. British Iron Age culture was an oral one: they did not write down their stories, thoughts or histories. As such, what we know about the tribes comes from archaeologyThe study of the things humans have left behind. See 'Some Notes of Archaeology'. and from outside observers, including Julius Caesar. It is therefore difficult to build a firm picture of them, their history, or their way of life: it is easy for outsiders to be mistaken or confused by different practices, or to misrepresent them deliberately to show British inferiority and outside (Greek or Roman) superiority.

Reasons for Caesar’s invasion

Despite its trade links, the Romans saw Britain, whose 'sky is obscured by continual rain and cloud', Tacitus, Agricola 1.12 as on the edge of the known world, and at first glance it would seem an unlikely target for their aggression. There was unrest in Rome, and trouble in its provinces and along its borders, so surely the Romans had enough to be doing. What then motivated Caesar to pick an illegal fight with an island so far removed from civilisation? Firstly, and importantly in the eyes of the average Roman, Caesar claimed it was self defence. He invaded Britain to protect Rome. As he said in his Gallic Wars, 'He made this decision because he found that the British had been aiding the enemy in almost all our wars with the Gauls'. Caesar always wrote about himself in the third person. Many of the quotations used in this article are taken from Caesar's Gallic Wars, books four and five. However, I will not reference them all, to reduce the number of notes used. Other sources will still be referenced. With trading and cultural connections between Gaul and south-eastern Britain, it was natural for Britain to support Gaulish resistance, and if the Britons were offering aid to the enemy, Caesar wasn't starting a new war, but pursuing victory over Gaul. It is worth noting that Rome, that great conquering empire, had officially never led an offensive war. Every war it entered was defensive, and justified by one of four main reasons – i) ‘liberating’ a people, even when there was no treaty of defence in place; ii) responding to a request for help from a friend (such as during the Claudian invasion of Britain); iii) protecting assets that it already owned, but which were accepting outside help (such as in Julius Caesar's invasion of Britain); and iv) in response to a direct threat or insult (which could be very minor).

The Roman Republic at the death of Caesar
The Roman Republic at the death of Caesar


Despite their need to justify war, Rome was a state that survived on conquest. It needed the spoils of war (in taxes, slaves, and other items) to keep it functioning. By the Late RepublicA time in ancient Rome lasting from about 150BCE until the assumption of power by Octavian in 30BCE. It covers a period when the foundations of the Republic became more shaky, with 'great men' achieving dominance and often ignoring the laws and traditions of the Senate., the city of Rome was not self-sufficient, and was constantly under pressure from its increasing size. The plebeian masses could be terrifying: imports of cheap wheat and other foodstuffs were required to keep them from starving and rioting, and the legions demanded payment, in cash or in land. Conquered territories could provide both.

There were also personal reasons for Julius Caesar's invasion of Britain. He had no doubt heard about the riches in the British Isles, known for the 'gold and silver and other metals', Tacitus, Agricola 1.12 that the Britons had traded with the Continent for centuries. In the Late Republic, the spoils of war were shared between the state, the conquering generals, and - to a lesser extent - their soldiers, and Caesar, as a politician who knew how to gamble and had racked up significant debts in his climb to the top, needed the money.More infoTechnically, the spoils of war that weren't immediately given to the state were kept in trust by the conquering general, but some amount of light-fingeredness was a fact of life. There were limits, though: in 70 BCE, Cicero successfully prosecuted the governor of Sicily, Gaius Verres, for excessive plundering and thus of depriving the state of what was rightfully its own. But more than money, he needed power and publicity. The publicity was one reason for his reports on the wars: it kept him in the public eye where he was able to present his version of events in a more favourable light. However, Caesar was prepared to discuss his own mistakes, and the Gallic Wars is noted for its honesty. Greatness in Rome was measured by great deeds, judged against those of the ancestors and other men, and Caesar wanted to be great. Plutarch reports that:

When free from business in Spain, after reading some part of the history of Alexander, he sat a great while very thoughtful, and at last burst out into tears. His friends were surprised, and asked him the reason of it. "Do you think," said he, "I have not just cause to weep, when I consider that Alexander at my age had conquered so many nations, and I have all this time done nothing that is memorable."More infoPlutarch’s Caesar, translated by John Dryden

Caesar wearing a general's cloak
Caesar wearing a general's cloak

There were other, more pressing, reasons for the invasion. Having already acted in a legally questionable manner during his consulship, His consulship in 59 BCE, which he shared with Marcus Bibulus, had been marked by a number of irregularities, not least the way in which Bibulus was hounded to the point where he refused to leave his house and Caesar was able to force through legislation by himself. 59 BCE came to be known by Roman commentators as the year of 'the consulship of Julius and Caesar'. Caesar was aware that once he returned to Rome he could be prosecuted, and he had enough enemies to make him nervous of the outcome. Prosecutions were brought by wealthy individuals rather than the state, and there were many wealthy individuals, such as Cato the Younger, who did not like Caesar. Cato, for example, suggested sending Caesar back to the tribes of the million or so people Caesar was said to have killed during the Gallic Wars. The successful invasion of somewhere so distant, so barbaric, and yet so rich would not only win him further popularity with the people, it would also make his case in the Senate stronger. It might even allow him a further extension as governor, delaying any hopes his enemies might have of prosecuting him. But the British campaign was also politically dangerous, as he would be campaigning outside the territory assigned to him, and in crossing the Channel he was making one of his well-placed political gambles.

55 BCE: Caesar's first invasion

Caesar intended to cross to Britain in 56 BCE, but was delayed first by a Gaulish rebellion in modern-day Brittany and the area around Calais, and then by German incursions across the Rhine. These incursions were in fact two tribes of refugees, which asked Caesar for help. After a skirmishSmall and unplanned bouts of fighting., which they allegedly started, Caesar had the majority of the refugees - including women and children - massacred. The site where this happened has recently been discovered, and you can read about it here. Strabo claimed the Gaulish uprisings were a deliberate attempt to disrupt the invasion of Britain, as it was in the Gauls' interest to delay it and forewarn the British tribes. Furthermore, Gaulish traders refused to provide any useful intelligence on Britain to Caesar, beyond hazy details about coastal areas and that portion of the island immediately opposite Gaul. Some have argued that this merely shows Britain's isolation from the rest of Europe during the late Iron Age, although the Gallic warnings, and the alleged British help to the Gauls, would contradict this. Caesar complained that:

He could not learn from them the size of the island, or how many people or nations inhabited it, or what system of warfare they practised, or what customs they followed, or where harbours might be located suitable for a big fleet of large ships.

Caesar's first invasion, drawn by Edward Armitage
Caesar's first invasion, drawn by Edward Armitage

Thanks to the warnings from the Gauls, the British tribes were well-prepared when Caesar's first fleet of eighty transport ships, carrying two legions, About 10,000 men in total – this was in the days before Augustus’ standardisation of the army entered British waters. The tribes had been forewarned not just by the Gaulish merchants, but also by Caesar sending an ambassador, Commius of the Atrebates, to them. Commius was promptly thrown in chains and held until the arrival of Caesar. The defenders stood at the cliff tops and, for a while, succeeded in holding off the Romans with slings and darts. The Romans, harassed and concerned about leaping fully armoured into deep water, were unwilling to meet the enemy. They lingered on board until the standard bearer of the tenth legion jumped off the boat shouting 'Leap, fellow soldiers, unless you wish to betray your eagle to the enemy. I, for my part, will perform my duty to the Republic and my general'. Shamed, the rest of the legionaries followed and the two armies met in the shallows in chaos and confusion.

The fighting seemed to go the way of the Britons, until Caesar ordered shallower-bottomed ships to carry more troops to dry land, at which point the tribes turned and fled. They were not pursued far: the Romans had no cavalryPeople fighting on horseback, who were therefore more mobile than foot soldiers. In modern warfare, the cavalry are those fighting in armoured vehicles.. Following this defeat, representatives of the British tribes sued for peace, promising payment of a tribute and providing hostages.More infoThis was standard Roman procedure, which ensured obedience to Rome (by risking the lives of the hostages if not) and Romanising the next generation, thus making them look upon Rome more favourably.

It had not been Caesar's plan to invade without cavalry, and 18 transport ships had been arranged to carry them, but when

they were approaching Britain and were seen from the camp, so great a storm suddenly arose that none of them could maintain their course at sea; and some were taken back to the same port from which they had started;-others, to their great danger, were driven to the lower part of the island, nearer to the west; which, however, after having cast anchor, as they were getting filled with water, put out to sea through necessity in a stormy night, and made for the continent.

The Romans, up until this point, had been used to the calm waters of the Mediterranean, which provided a stark contrast to the choppy waters of the Channel. The sudden arrival of the storm would have seemed almost magical to the Romans, or a sign of an unhappy god. Some thought that the DruidsThe name given to priests of an Iron Age system of beliefs in Britain and Gaul., who allegedly worked weather magic (similar to the Cornish wreckers of the 17th and 18th centuries), pulled up this weather to halt the invasion. This was confirmed by further bad omens: as Caesar disembarked, he fell, getting a mouthful of sand. The Romans were very aware of omens before battle, although they could stubbornly overlook them. In one famous incident, a standard dropped, soldiers were given food usually offered to the dead at funerals, and their commander, Crassus, accidentally dropped the entrails of the last general sacrifice. Shortly afterwards, Crassus marched his seven legions (about forty thousand men) into the Battle of Carrhae. Twenty thousand were killed, ten thousand were captured and only ten thousand escaped. Crassus and his generals were killed. Some say that Crassus was killed when the Parthians poured molten gold down his throat, although if this happened, it was after he had already died in battle (according to Cassius Dio). However, Plutarch says that his head was cut off and used as a prop in a play. Typically, however, Caesar managed to turn this bad omen to his advantage, saying he already had Britain in his grasp. The bad weather and rough sea didn't just affect the cavalry transports. Water filled the infantrySoldiers who fight on foot. transport and warships, and the sea sent them crashing together, wrecking many. Those that did survive were not fit for sailing.

Despite their initial 'victory' the Romans were stranded on their beachhead without provisions or resources for repairing their only means back to Gaul. The British tribes seized their chance, employing guerrilla tactics and attacking foraging parties. The situation quickly turned to stalemateWhere neither opponent can make a move or win.: the Britons could not match the Romans in open battle, and couldn't retake the beach, but nor could the Romans move beyond it. Ambassadors were again sent to Caesar, promising fresh tribute and hostages, but Caesar, needing to return to the Continent before winter, asked for them to be sent after him. Caesar, his ships once again seaworthy, departed soon afterwards and was granted 20 days of thanksgiving by the Senate, an unusual honour and one which encouraged him to return the following year.

The 54 BCE invasion

The memorial at Walmer Beach, where Caesar is thought to have landed.
The memorial at Walmer Beach, where Caesar is thought to have landed.

When Caesar did return, it was with a greater and improved invasion force adapted from the lessons he'd learnt the previous year. Eight hundred ships designed by him, with shallower and broader hulls for easier beaching, carrying five legions, two thousand cavalry and a number of traders After an uncontested landing, Caesar continued through Kent. He met British tribes probably somewhere on the River Stour, but pushed them back to a hillfort, where they scattered. Unwilling to push his luck with night falling in unknown territory he made camp, only to find that his fleet had again suffered from bad weather. Forty ships at anchor in the Channel had been wrecked and others damaged by a storm and high tides. A temporary return to the coast was needed, where he sent word for more ships and his men spent 10 days and nights repairing those they could.More infoThis is also the time Caesar learned that his daughter, Julia, had died in childbirth. Julia had been married to another triumvirA member of a triumvirate., Pompey, and it was their shared care for her that cemented their own relationship. Within two years of her death, their relationship was falling apart, and Caesar and Pompey would eventually be on opposite sides of a civil war that ultimately led to Pompey’s death at the hands of Egyptians in 48 BCE.

When Caesar returned to the Stour, he found the tribes had used the time to organise their resistance under Cassivellaunus, a powerful warrior king of (probably) the Catuvellauni tribe. The Romans have naturally painted Cassivellaunus as an expansionist and destabilising influence, who had intimidated and conquered his neighbours, thus providing Rome with a further excuse for fighting. After a few skirmishes, Cassivellaunus realised he couldn't defeat the Romans in pitched battle and again resorted to guerrilla tactics. He used chariots and superior knowledge of the territory to delay the Roman army on their march north, giving the British time to fortify the only fordable place on the River Thames. The British use of chariots was enough to frighten the Romans and impress Caesar, who described their tactics in the Gallic Wars:

First they drive in all directions hurling spears. Generally they succeed in throwing the ranks of their opponents into confusion just with the terror caused by their galloping horses and the din of the wheels. They make their way through the squadrons of their own cavalry, then jump down from their chariots and fight on foot. Meanwhile, the chariot drivers withdraw a little way from the fighting and position the chariots in such a way that if their masters are hard-pressed by the enemy’s numbers, they have an easy means of retreat to their own lines. Thus, when they fight they have the mobility of cavalry and the staying power of infantry: and with daily training and practice they have become so efficient that even on steep slopes they can control their horses at full gallop, check and turn them in a moment, run along the pole, stand on the yoke, and get back into the chariot with incredible speed.

The fortification of the Thames was not enough to prevent the Romans crossing it. One second century Macedonian author, Polyaenus, suggests that Caesar used an elephant to scare away the tribes. Caesar himself makes no reference to an elephant, merely stating that 'the soldiers advanced with such speed and such ardour...that the enemy could not sustain the attack of the legions and of the horse, and quitted the banks, and committed themselves to flight'. The point was proved, though: the tribes fought best in small numbers using the land to their advantage, and open battle should be avoided.

Coin using tribes of south eastern England in the late Iron Age.
Coin using tribes of south eastern England in the late Iron Age.

British tribal life was fraught with internal conflicts and rivalries. Cassivellaunus had recently conquered the Trinovantes, in what is now Essex, forcing their prince, Mandubracius, into exile. Mandubracius, sensing a powerful potential allyA state (or person) that is formally working with another state (or person), usually confirmed by a treaty or other official agreement. in Caesar, approached Caesar and agreed a peace in return for his restoration to the Trinovantes under the protection of Rome. Cunliffe argues it was likely this peace was agreed in advance of the Thames crossing, as Caesar wouldn't have pushed so quickly into enemy territory so far from his supply base without being sure of success. The Trinovantes would send 40 hostages to Rome and grain for the army, as well as providing much needed information. Five other tribes, These tribes were the Cenimagni, Segontiaci, Ancalites, Bibroci and Cassi. seeing the protection given to the Trinovantes against violence and pillage, followed suit, also providing provisions and information, including the location of Cassivellaunus' stronghold. A siegeA military operation in which enemy forces surround a town or building, cutting off essential supplies, with the aim of compelling those inside to surrender. was laid and, after a diversionary attack on the Roman's beachhead failed, Cassivellaunus surrendered. 

With trouble brewing on the Gaulish front, Caesar left without fulfilling the conquest (if he ever meant to), but with treasure and treaties from a few tribal chiefs, as well as the British hostages. Caesar's acknowledged reason for the invasion, to prevent the Britons from helping the Gauls, succeeded: there is no further reference to the British fighting in their defence.

The legacy of Caesar's invasion

Caesar’s immediate effect on Britain was little, but he brought the island to the attention of Rome and into her sphere of influence. The south east of Britain, at the very least, developed closer ties with the Roman world. Trade between Britain and Rome increased, and children of the elite were educated in Rome, enhancing the tribes' RomanitasA Latin word used to describe the set of political and social ideas and practices that the Romans used to define themselves. Those without Romanitas were considered barbarian., or Romanisation. Trade increased so much that the focal point between Britain and the outside world changed, with that of the Atlantic zone, focused on Hengistbury Head, lessening dramatically in favour of the Dover-Calais Strait.  Rome now had a political investment in Britain: the Trinovantes were technically left as a protectorateThe position or period of office of a Protector, especially that of Oliver and Richard Cromwell in England., Mandubracius was given special trade rights and privileges while Rome became a refuge for other exiled tribal leaders, In about 10 CE'Common era', the non-religious way of saying AD ('anno Domini', or 'the year of our lord')., two British leaders, Tincomarus and Dubnovellaunus, fled there. and Strabo tells us that a number of British chieftains paid homage to Augustus following the civil war. UnRoman Britain argues there was also military investment in the island, with evidence for Roman troops being posted in the client lands of Britain before the Claudian invasion of 43 CE. Whether these troops were there to protect the interests of clients, to intimidate, to prepare for a more formal incursion, or for a combination of reasons cannot be known. Julius Caesar's invasion made it possible, 100 years later, for a tribal chief to appeal to Rome for help, and for the Roman Empire to seize that excuse for the full-scale invasion and annexation of Britain.

Things to think about

  • Was it wise of Caesar to invade?
  • Did the Gauls want to help Britain fight Caesar?
  • What does his invasion tell us about Caesar as a man and a general?
  • What does Caesar's invasion tell us about the health of the Late Roman Republic?
  • What effect did Caesar's invasion have on Britain?

Things to do

  • Although there is no archaeological evidence for Caesar's landing in Britain, he is believed to have landed on either Deal or Walmer beach in Kent. There is a memorial stone at Walmer beach which you can visit. Whilst there, look around and see how easy - or difficult - it would have been to land an invasion force there.

Further reading

For those wanting to understand Rome during the Late Republic, Tom Holland's Rubicon: The Triumph and Tragedy of the Roman Republic provides a good introduction. Caesar's Gallic Wars, books four and five are an extremely important source for understanding Caesar's invasion of Britain. There are a number of translations available for free on the internet (such as this one), including in Latin for the brave, or you can buy it from Amazon.

Author Info

Debbie Kilroy

Having read history at the University of Birmingham as an undergraduate, where I won the Kenrick Prize, I worked as a trouble-shooter in the public sector until I took a career break in 2009. Thereafter, I was able to pursue my love of history and turn it into a career, founding Get History in 2014 with the aim of bringing accessible yet high quality history-telling and debate to a wide audience. Since then, I have completed a Masters in Historical Studies at the University of Oxford, from which I received a distinction and the Kellogg College Community Engagement and Impact Award. As well as continuing to write for and expand Get History, I am now a freelance writer and historian. I have worked with Histories of the Unexpected and Inside History, and my article for Parliaments, Estates and Representation won the ICHRPI Emile Lousse essay prize (2019).