[Martin Kallander]

Over the course of the roman empire there were three emperors named Ioannes. Ioannes I (423-425), Ioannes II (969-976) and Ioannes III (1118-1143). For some reason we in the modern day call the first one Ioannes, but translate the other two to John and start counting from Ioannes II as John I and Ioannes III is called John II. What is the reason for doing this? It makes very little sense to me

edit*
There were a whole lot more emperors named Ioannes than I thought. After the fourth crusade just about every emperor and his grandmother was named Ioannes apparently which brings the number up to 9 if you count the Ioannes that reigned in the 5th century. (again I don't see why you would not)

[Walter Stockwell]

There wasn't one "Roman Empire". Ionnes I (423-425) was emperor of the Western Roman Empire. The others were emperors of the Eastern Roman Empire. The eastern Johns wouldn't have recognized the Ionnes from the western empire as predecessors.
Just my superficial knowledge of the Romans...

[Martin Kallander]

That doesn't explain why we call the later ones John but not the first one. The division of the empire really is overrated in the modern day as well, Ioannes reign ended because the eastern emperor, Theodosius II sent armies to depose him and replaced him with Valentian, his 5 year old caesar.

[Jonathan Blair]

Per Wikipedia:

[Martin Kallander]

[Jonathan Blair]

[Sean Manning]

Last time I checked, I could not trace regnal numbers before the 16th century or maybe the 14th. Ancient Babylonian and Greek scholars used bynames (Ptolemy Soter, Philip the Handsome) or filiations (Dareios the son of Artaxerxes, Alexander the son of Philip) to distinguish between kings with the same name. But then sometimes you get nine Ptolemies Soter, or three King Edwards in a row, and some scholar thought of using numbers to distinguish them.

Like Jonathan says, when scholars create lists of kings for scholarly purposes, they are making decisions about who counts and who does not. The next scholar can make different choices (especially if the last king of the last dynasty suffered a tragic accident and the executioner will be present when they present the results of their work to the new king!)

In scholarly books, deciding between Greek, Latin, and modernized forms of names is a stylistic choice like American versus British spelling.

[Martin Kallander]

[Mark Millman]

Dear Martin,

The real answer, I suspect, is that some prominent historians, who most probably did not discuss all three emperors at the same time or as a group at all, did it that way--I imagine this would have been well back in the nineteenth century, but it could have been more recent--and it stuck. Such trend-setting historians very likely specialized in either Western or Eastern Roman history, and so would have adopted their conventions independently. Once those conventions became accepted practices it would have been more confusing to change. I don't think you're going to find a more satisfying answer. People simply aren't consistent.

One distinction that seems fairly apparent, however, is that the first was a Latin emperor and the following two were Greek. You could, in the absence of any other likely reason, relate it to the need or lack thereof to translate from Greek and Latin respectively.

I hope this proves helpful . . . because otherwise it seems likely that you'll remain frustrated unless you want to read a lot of histories of and papers about the Roman state. Though if you're looking for a dissertation topic in historiography, this might not be a bad one.

Best,

Mark Millman

[Sean Manning]

[Martin Kallander]

[Sean Manning]