the eastern augustus, in order to keep the balance of power in the imperium, elevated Galerius as his caesar, possibly on 21 May 293 at Philippopolis (Plovdiv). Constantius was the more senior of the two caesares, and on official documents he always took precedence, being mentioned before Galerius. Constantius' capital was to be located at Augusta Treverorum (Trier). Constantius' first task on becoming caesar was to deal with the Roman usurper Carausius who had declared himself emperor in Britannia and northern Gaul in 286. In late 293, Constantius defeated the forces of Carausius in Gaul, capturing Bononia (Boulogne-sur-Mer). Carausius was then assassinated by his rationalis (finance officer) Allectus, who assumed command of the British provinces until his death in 296. Constantius spent the next two years neutralising the threat of the Franks who were the allies of Allectus, as northern Gaul remained under the control of the British usurper until at least 295. He also battled against the Alamanni, achieving some victories at the mouth of the Rhine in 295. Administrative concerns meant he made at least one trip to Italy during this time as well. Only when he felt ready (and only when Maximian finally came to relieve him at the Rhine frontier) did he assemble two invasion fleets with the intent of crossing the English Channel. The first was entrusted to Julius Asclepiodotus, Constantius' long-serving Praetorian prefect, who sailed from the mouth of the Seine, while the other, under the command of Constantius himself, was launched from his base at Bononia. The fleet under Asclepiodotus landed near the Isle of Wight, and his army encountered the forces of Allectus, resulting in the defeat and death of the usurper. Constantius in the meantime occupied Londinium (London), saving the city from an attack by Frankish mercenaries who were now roaming the province without a paymaster. Constantius massacred all of them. Constantius remained in Britannia for a few months, replaced most of Allectus' officers, and the British provinces were probably at this time subdivided along the lines of Diocletian's other administrative reforms of the Empire. The result was the division of Britannia Superior into Maxima Caesariensis and Britannia Prima, while Flavia Caesariensis and Britannia Secunda were carved out of Britannia Inferior. He also restored Hadrian's Wall and its forts. Later in 298, Constantius fought in the Battle of Lingones (Langres) against the Alemanni. He was shut up in the city, but