Constantine the Illyrian(?)

Constantine "the Great" is constantly called an Illyrian emperor in articles. Other posts try to refute this, mentioning he was not born in Illyricum, and born well after the Illyrians were overwhelmingly integrated into the Roman sphere. Some of these articles claim he was descended from an Italian family that colonized the Roman city. The man is directly or indirectly responsible for our current calendar, Sundays off, knees bent to Mary, and on and on. He's on par with or more impactful to European history than Genghis Khan, Charlemagne, he's Constantine after all. A number of people groups want to claim his legacy as part of their own, understandably so. He spoke Latin, his mother was Greek, his father a highly regarded military leader. 

Just how “Illyrian” (or not) was the guy?

His descendants appear to have commissioned a fabricated genealogy well after his death, linking him with a few noteworthy Italian families, but this was most certainly done to justify their own right to rule in a manner more rational than “divine right” as was common, but evident to be little more than clout chasing.

Just as slaves in the Americas often took their master’s surnames upon their freedom, or the family name of a neighbor or good Samaritan, so the colonists in Rome would end up taking the family name of the colony’s founders, in the case of Naissus (Nis, Serbia), the Flavian dynasty.

More likely than the posthumous writing that Constantine descended directly from a family from the Italian Peninsula, his paternal line was autochthonous according to a myriad of historians (seemingly most). It is recorded that the Dardani occupied the region prior to the founding of the Roman colony at modern day Nis. The Dardani are recorded as an Illyrian tribe with Thracian elements.

It would appear then, that based on the best available data, Constantine was most certainly and obviously Roman, although descended from indigenous constituents, in this case an Illyrian, or possibly Thracian/Thraco-Illyrian.

Finding out what haplogroup he was is impossible at this point in history. But whatever he and his father were, their campaigns along the Rhine and into Britain no doubt facilitated the further spread of Illyrian associated haplogroups, such as J-L283 throughout western Europe. Since he and his father are both recorded as being born at what is now Nis, Serbia, and his father would be well-acquainted with the locals, it is likely his father’s campaigns favored locals as well, again, enabling the further spread throughout Europe of males of Illyrian descent. Constantine’s father died in the region of modern day York, in Britain.

Inside the Roman era, approximately 395 CE, J-L283 is buried northwest of Nis. Romans of Illyrian descent were definitely in the region during the era Constantine was born.