After Caesar's expeditions, the Romans begin their real attempt to conquer Britain in CE 43, at the behest of the Emperor Claudius.

They land in Kent, and defeat two armies led by the kings of the Catuvellauni tribe, Caratacus and Togodumnus, in battles at the Medway and the Thames.

Togodumnus is killed, and Caratacus flees to Wales.

The Roman force, led by Aulus Plautius, now halts as Plautius sends for Claudius to come and finish the campaign.

When Claudius arrives he leads the final march on the Catuvellauni capital at Camulodunum (modern Colchester), before returning to Rome again for his triumph.

The Catuvellauni at this time hold sway over most of the southeastern corner of England; eleven local rulers surrender, a number of client kingdoms are established, and the rest become a Roman province with Camulodunum as its capital.

Over the next four years, the territory is consolidated and the future emperor Vespasian leads a campaign into the Southwest, where he subjugates two more tribes.

Caligula’s Northern Campaign and the Aborted Invasion of Britain (40 CE)

The northern campaign of Emperor Caligula in 40 CE, intended as an invasion of Britain, was ultimately abandoned, leading to widespread mockery from ancient historians. Accounts describe his troops gathering seashells as "spoils of war", and his triumph in Rome featuring Gauls dressed as Germanic captives. However, modern historians dispute the nature and purpose of this expedition, offering alternative explanations.

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Possible Explanations for Caligula’s Actions

Since primary sources differ, historians have put forward several theories:

1. A Training and Scouting Mission

   • The journey to the English Channel may have been a preliminary reconnaissance for a future invasion.
   • It is possible that Caligula intended to test logistics and troop movements before launching a full-scale campaign.

2. A Diplomatic Encounter: The Surrender of Adminius

   • Adminius (Amminus), son of Cunobelinus, the king of the Cantiaci in eastern Kent, had been exiled by his father around 39–40 CE.
   • He fled to continental Europe with a small group of followers and surrendered to the Romans.
   • Caligula may have exaggerated this event, claiming it as a great victory over Britain.
   • He even had an extravagant report read before the Senate, declaring a triumph over "foreign tribes."

3. Interpretations of the "Seashells" Incident

   • Suetonius and Dio Cassius mock Caligula for ordering his troops to collect seashells, supposedly as spoils of war.
   • Some modern historians suggest "seashells" (conchae in Latin) could be a metaphor for:
     • Boats, meaning that Caligula’s troops had captured British ships.
     • Female genitalia, implying the troops were visiting brothels.

4. A Potential Mutiny at Boulogne

   • Another theory is that Caligula’s troops refused to embark on the invasion, leading to a breakdown in the campaign.
   • Roman legions had previously shown reluctance to cross into unknown territories, and a mutiny could explain why the invasion was abandoned.

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Adminius’ Exile and Its Political Consequences

• Cunobelinus, King of the Cantiaci, had maintained friendly relations with Rome, but by 40 CE, an anti-Roman faction may have emerged in Britain.
• His other sons, Togodumnus and Caratacus, might have forced Adminius out of power, consolidating an anti-Roman resistance.
• Alternatively, the Cantiaci could have revolted against Cunobelinus’ rule, prompting Adminius’ flight to the Romans.

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The Failure of Caligula’s Expedition and Its Long-Term Effects

• Caligula’s refusal to return Adminius to his father contributed to growing anti-Roman sentiment in Britain.
• This eventually led to increased hostilities, necessitating the successful Roman invasion under Claudius in 43 CE.
• While Caligula’s ambitions in Britain failed, his actions planted the seed for later Roman intervention.

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Conclusion: A Misunderstood Expedition?

• While ancient historians derided Caligula’s British campaign, modern scholars suggest it may not have been as absurd as depicted.
• His gathering of seashells and triumph in Rome were likely propaganda efforts to maintain prestige, masking the invasion’s failure.
• Ultimately, his expedition proved inconsequential, but it foreshadowed Rome’s inevitable conquest of Britain under Claudius.

Though remembered as an eccentric display of imperial delusion, Caligula’s campaign to Britain in 40 CE may have been a stepping stone for Rome’s eventual annexation of the island three years later.

The most far-reaching of Claudius’s expansions of imperial territory is the conquest of Britannia.

Claudius in 43 sends Aulus Plautius with four legions to Britain (Britannia) after an appeal from an ousted tribal ally.

Britain is an attractive target for Rome because of its material wealth—particularly mines and slaves.

It is also a haven for Gallic rebels and the like, and so could not be left alone much longer.

Aulus Plautius, aiming to subdue the intransigent tribal kingdoms, invades with an army of twenty thousand, crossing the English Channel to land at Rutupioae (present Richborough, Kent), an important natural harbor.

The Catuvellauni and Trinovantes warriors, surprised and defeated, retreat toward …

…the region of present London but suffer a second defeat near Durobrivae (present Rochester).

Cunobelinus, Catuvellauni overlord of southeastern England, had died prior to the Roman invasion under Aulus Plautius in 43; his sons Caratacus and Togodumnus lead the British defense, using guerilla tactics against an estimated forty thousand troops.

They lose much of the southeast after being defeated in two crucial battles on the rivers Medway and Thames.

The Roman commander then secures a crossing point of the River Thames, halts, and sends word for Claudius to join him for the final march on the Catuvellaunian capital, Camulodunum (Colchester).

Dio says that this was because the resistance became fiercer as the Britons tried to avenge Togodumnus, and Plautius needed the emperor's help to complete the conquest; however, as Claudius was no military man and in the end spent only sixteen days in Britain, it is likely the Britons were already as good as beaten.

Claudius arrives with reinforcements, including artillery and elephants, which must have made an impression on the Britons when they were displayed in the large tribal center of Camulodunum.

As Suetonius and Claudius' triumphal arch state, the British kings surrendered without further bloodshed.

An alternative reading of Dio's history of the invasion suggests that Togodumnus may actually have been acting in support of the Roman troops, against his brother Caratacus, and that he survived the battles of the River Thames, providing the later Roman administration with valued assistance.

Dr. Miles Russell of Bournemouth University has further suggested that Togodumnus and Tiberius Claudius Cogidubnus, whose original name may have been Togidubnus or Togodumnus, postulated resident of the late first century CE palace at Fishbourne may well have been one and the same.

Claudius is present in August when his legions march into Camulodunum (Colchester), the capital of the Catuvellauni, but Caratacus survives and carries on the resistance further west.

Caractacus rallies the Silures and Ordovices to the cause, but separate Roman expeditions crush the rebels, and other tribes readily accede to Roman sovereignty; he will remain at large until 51.