Editing List of Roman emperors (section)

=== List inclusion criteria ===
Given that a concept of constitutional legitimacy was irrelevant in the Roman Empire, and emperors were only 'legitimate' in so far as they were able to be accepted in the wider empire,{{Sfn|Omissi|2018|p=34}} this list of emperors operates on a collection of inclusion criteria:

* Imperial claimants whose power across the empire became, or from the beginning was, absolute and who ruled undisputed are treated as legitimate emperors.{{Sfn|Omissi|2018|p=32}} From 286 onward, when imperial power was usually divided among two colleagues in the east and west,{{Sfn|Omissi|2018|p=xix}} control over the respective half is sufficient even if a claimant was not recognized in the other half, such as was the case for several of the last few emperors in the west.{{Sfn|Mathisen|1997}}
* Imperial claimants who were proclaimed emperors by another, legitimate, senior emperor, or who were recognized by a legitimate senior emperor, are treated as legitimate emperors.<ref>{{Harvnb|Omissi|2018|p=25}}; {{Harvnb|Claes|2015|p=18}}.</ref> Many emperors ruled alongside one or various joint-emperors. However, and specially from the 4th century onwards, most of these were children who never ruled in their own right. Scholars of the later Empire always omit these rulers,<ref>{{Harvnb|Foss|2005|p=101}}; {{Harvnb|ODB|p=360}}.</ref> but the same is not always applied during the early Empire.{{Sfnm|1a1=Elton|1y=1825|1p=303|2a1=Grant|2y=1998|2p=179|3a1=Hekster|3y=2008|3p=155|4a1=Cooley|4y=2012|5a1=Kienast|5a2=Eck|5a3=Heil|5pp=v-xii|6a1=Britannica|7a1=Livius|8a1=MET}} For the purposes of consistency, later senior emperors' tenures as junior co-emperors are not counted as part of their reign. The list also gives all co-emperors their own entry only up to the 4th century.
* Imperial claimants who achieved the recognition of the Roman Senate, especially in times of uncertainty and civil war, are, due to the senate's nominal role as an elective body, treated as legitimate emperors.<ref>{{Harvnb|Claes|2015|p=15}}; {{Harvnb|Omissi|2018|p=17}}</ref> In later times, especially when emperors ruled from other cities, this criterion defaults to the possession and control of Rome itself. In the later eastern empire, possession of the capital of [[Constantinople]] was an essential element of imperial legitimacy.{{Sfn|Van Tricht|2011|pp=79–80}}
In the case of non-dynastic emperors after or in the middle of the rule of a dynasty, it is customary among historians to group them together with the rulers of said dynasty,{{Sfn|Lawler|2004|p=323}} an approach that is followed in this list. Dynastic breaks with non-dynastic rulers are indicated with thickened horizontal lines.