Empresses regnant in the context of "Pro tempore"

The term Roman empress usually refers to the consorts of the Roman emperors, the rulers of the Roman Empire. The duties, power and influence of empresses varied depending on the time period, contemporary politics and the personalities of their husband and themselves. Empresses were typically highly regarded and respected, and many wielded great influence over imperial affairs. Several empresses served as regents on behalf of their husbands or sons and a handful ruled as empresses regnant, governing in their own right without a husband.

Given that there were sometimes more than one concurrent Roman emperor, there were also sometimes two or more concurrent Roman empresses. For most of the period from 286 to 480, the Roman Empire, though remaining a single polity, was administratively divided into the Western Roman Empire and the Eastern Roman Empire. Through most of this period, the separated imperial courts had their own lines of succession, and as a result their own sequences of concurrent Roman empresses. The western empire fell in the late 5th century, its final empress being the wife of Emperor Julius Nepos. The eastern empire, often referred to as the 'Byzantine Empire' by modern historians, endured for almost another millennium until its fall through the fall of Constantinople in 1453. The final empress of the east, and final Roman empress overall, was Maria of Trebizond, wife of Emperor John VIII Palaiologos.