In Britain the start of Commodus' reign saw serious fighting, some of the worst of his reign. According to Cassius Dio, enemy tribes crossed the Wall that divided them from the Romans, cut down a Roman General (probably the governor of Britain) and the troops he had with them and ravaged widely. The Wall is almost certainly Hadrian's Wall and some sites show signs of destruction from this period. Commodus eventually sent Ulpius Marcellus to take action. An austere an incorruptible man with a reputation as a severe disciplinarian, Marcellus led a number of punitive campaigns into southern Scotland, exacting a terrible retribution on the tribes there.
The war also came as a bad shock to the civilian population of Britain. Before the end of the 2nd century only a few towns in Britain had any defences, the Emperors disliked providing strong holds for potential rebellions, now many settlements started to build earthen ramparts around them. The construction of these defences does not seem to have been done in haste, suggesting a threat that was real but not imminent. These walls, later rebuilt in stone, were in stark contrast to the undefended cities on the continent. The absence of city walls here was to prove disastrous in the great barbarian attacks in the late third century.
One unfortunate development in Commodus' reign was the increasing political power of the Roman army in Britain. In AD 185 a 1500 man delegation had been sent to Rome to demand that the Praetorian prefect (a powerful figure who Commodus had left in charge of much of the governance of the Roman empire) and surprisingly succeeded! Commodus later sent Pertinax to take charge of the situation in Britain. Pertinax managed to deal with the ringleaders, but was nearly killed when a legion mutinied (Some of his bodyguard were killed and Pertinax left for dead). Pertnax punished the mutiny very severely but was eventually forced to resign because of the legions hostility to him.
The murder of Commodus and civil war.
Commodus was finally murdered in 193 AD and replaced by none other than Pertinax. Its easy to imagine the reaction of the army in Britain to this news. Pertinax however didn't last long, and after only three months was murdered by the Praetorian guard (Pertinax had failed to pay them their expected bonus). There followed one of the most notorious episodes in Roman history when the Praetorian guard auctioned the post of Emperor to the highest bidder, it was bought by the very wealthy senator Didius Julianus. However the disastrous chain of events was hardly over as the legions in Pannonia, Syria and Britain all proclaimed their commanders as Emperor.