205 A. D. he was executed on a charge of treason made by his own
son-in-law. At his death two prefects were again appointed, one of whom
was Papinian, the greatest of all Roman jurists. His appointment seems to
indicate a division between the military and the civil functions of the
prefecture. For from this time the prefect exercised supreme jurisdiction
over criminal cases in Italy beyond the hundredth milestone from the city,
and in the matter of appeals from the judgments of provincial governors.
In the absence of the princeps he also presided over the imperial judicial
council. Following Papinian other eminent jurists filled this office.
Furthermore, the supervision of the transportation of grain to Rome was
transferred from the prefect of the grain supply to the praetorian
prefect, and the former officer merely supervised its distribution within
the city.

*War in Britain, 208-211 A. D.* Like Hadrian, Severus paid great attention
to strengthening the frontier defences of the empire, particularly the
fortifications which linked the Rhine and the Danube. In 208 A. D. when
Britain was invaded by the Caledonians, he took the field, accompanied by
his two sons. He reinforced Hadrian's earthen wall between the Tyne and
the Solway by a wall of stone, and carried on guerilla warfare against the
tribes of the northern part of the island. However, they had not been
completely pacified when he died at York in February, 211 A. D., leaving
the principate to his sons, Caracalla and Geta, both of whom had
previously received the title of Augustus.

*Caracalla, 211-217 A. D.* The bitter enmity which had long existed
between the two brothers continued during a year of joint rule, and
divided the empire into rival factions. Then Caracalla, who had previously
sought to make himself sole ruler, succeeded in having Geta assassinated.
Many of the latter's friends, among them the prefect Papinian, were
executed. Caracalla was cruel and vicious, and displayed no capacity for
governing. He relied solely upon the goodwill of the soldiery and courted
their support by increased pay and lavish donatives. In 212 A. D., by the
famous Antonian Constitution (_constitutio Antoniniana_) he extended Roman
citizenship to all the provincials of the empire, except those who were in
a condition of vassalage, such as some of the barbarian peoples who had
been settled on waste lands within the Roman borders, and not citizens of
organized municipalities (_