 In case of emergencies, the power to appoint a dictator for a six-month term was introduced.Later, proconsuls and propraetors could be given an "imperium" by appointment of the senate.Whoever used the "imperium" to victoriously lead an army could acquire the title of imperator, which later became chief title of the emperors, who were formally included in the system as proconsuls over most (and the strategically most important) parts of the empire, chief senators, and popular tribunes without the title.