Caligula’s Expansion into Mauretania and the Failed Invasion of Britain (40 CE)

In 40 CE, Emperor Caligula sought to expand the Roman Empire, securing its hold over Mauretania and making an ambitious—though ultimately unsuccessful—attempt to invade Britain. His erratic behavior and eccentric actions during this campaign would become legendary, culminating in the bizarre "war against Neptune."

The Annexation of Mauretania

• Mauretania (modern Morocco and Algeria) had been a Roman client kingdom under King Ptolemy, a descendant of Cleopatra and Mark Antony.
• In 40 CE, Caligula ordered his assassination, annexing the kingdom into the Roman Empire.
• The former kingdom was divided into two new Roman provinces:
  1. Mauretania Tingitana (western region)
  2. Mauretania Caesariensis (eastern region)

This secured Rome’s control over North Africa’s western frontier and strengthened its military and trade networks along the Mediterranean coast.

The Failed Invasion of Britain and the "War Against Neptune"

• Caligula aimed to achieve military glory by invading Britain, a land beyond the reach of prior Roman conquests.
• However, before launching the actual campaign, his legions halted at the shores of Gaul, awaiting orders.

Caligula’s Bizarre Orders

• Instead of crossing the Channel to fight the Britons, Caligula declared war on Neptune, the Roman god of the sea.
• He ordered his troops to attack the waves, symbolizing his domination over the ocean.
• Soldiers were commanded to collect seashells, which were allegedly referred to as "spoils of war."

This display of eccentricity and apparent madness left his commanders and soldiers bewildered, further undermining his credibility.

Later Roman Conquest of Britain

• Despite Caligula’s failure, his successors Claudius and later emperors would successfully conquer Britain:
  • In 43 CE, Emperor Claudius launched a full-scale invasion, leading to the Roman annexation of Britain.
  • By the mid-2nd century CE, Rome had extended its control as far north as Scotland, fortifying the frontier with Hadrian’s Wall (122 CE).

Legacy of Caligula’s Military Campaigns

• His annexation of Mauretania permanently secured Roman control over the region, ensuring its integration into the empire.
• His failed invasion of Britain became one of the most infamous episodes of his rule, contributing to his reputation for madness and delusion.
• His successors—particularly Claudius—would later complete the conquest of Britain, fulfilling Rome’s longstanding ambition to subjugate the island.

While Caligula’s military campaigns were largely ineffective, they marked important moments in Rome’s expansion, setting the stage for future emperors to achieve what he could not.