Carausius proved to be an effective ruler and with the support of his fleet he was able to achieve his own empire and tried hard to gain the recognition of the legitimate emperors, Diocletian and Maximian, who were joint rulers of the empire.
London had always owed its position and importance as the link to Britain and the rest of the empire. Now as the centre of this new empire, it was facing political and economic isolation. Carausius, needing to keep and eye on any attempts of retrieval by the main emperors, must have spent most of his time in London and various building projects, particularly in the eastern part of the town, suggests a measure of confidence and prosperity.
He was supported by his troops and in order to be able to pay them, Carausius opened a mint somewhere in London to issue coinage. He issued new coins, increasing the metal content and making the coins more valuable to create a secure basis for trade. These coins bear a London mint mark (see Minted in later Roman London in Public life).
Carausius hoped to be accepted by the emperors at Rome and he deliberately chose subjects for his coins that he hoped would show a united front with his fellow emperors to the rest of the empire. However, it took several attempts by the legitimate emperors to oust Carausius. Maximian first tried unsuccessfully in AD 288-9; soon afterwards Carausius issued a coin showing the busts of the three emperors, Diocletian, Maximian and himself. The legend read ‘Carausius and his brothers’.
In AD293, the Roman Empire was divided into two. Each had an emperor and a junior emperor (Caesar). Constantius Chlorus was appointed as Caesar of the western empire. He attacked Boulogne and re-took northern Gaul. In the same year, Carausius was assassinated by Allectus, his financial advisor.
Now that the Gaulish coast had been returned to the empire, it made it impossible for the rebel troops to patrol the channel and protect the southern coastline of Britain.
It is possible that a major building near the former public baths was started in London by Allectus which may have been intended as his headquarters. The foundations of the monumental building (PET81 and QUV01) have been dated precisely by tree-ring dating to AD294-5 but the building was never completed.
In AD296 Constantius Chlorus formed a sizable army and built a fleet to win the province back and Allectus, taken unwares by the attack, was defeated and killed in battle somewhere near Silchester.
For a description of what was found during the excavations, see Headquarters of the British Empire? in Londinium Lite.