The Strategicon by Kekaumenos describes events in the Byzantine empire during the Macedonian dynasty. It has some very harsh remarks about the proto-Romanians, called back then Vlachoi. It is a manuscript written in the 1078 according to some researchers. He was the son in law of Nikoulitzas Delphinas the leader of the Vlach rebellion in Larissa of the 1066, the first one ever recorded. The chronicler must have been well informed about ethnicity since he had first account exposure to it though his wife
Set aside the almost injurious rhetoric against the Vlachs, the author slips into the text a few valuable information about those people. The origin of the Vlachoi that caused the Byzantines trouble in the Balkans in 1066 AD is mentioned at page 74 in the text. Next is a snapshot photo-copied from the "Cecaumeni Strategicon by B. Wassiliewsky and V. Jermstedt published by Adolf M. Hakkert, Amsterdam 1963"
The translation of the second paragraph is
"The Vlachs never kept their word to anyone ,not even the ancient roman emperors. Having been attacked in war Emperor Trajan and having been totally defeated, they were subdued and their King, Decebal, was killed and his head was put on a pike and brought to the city of the Romans. These Vlachs are, in fact, the so-called Dacians, also called Bessians (Bessoi). Earlier they lived in the vicinity of the Danube and and Saos, a river which we now call Sava,where the Serbians live today. And later withdrew to their inaccessible fortifications. Relying upon these fortifications, they feigned friendship and submission to the ancient Roman Emperors and then swept down from their strongholds and plundered the roman provinces. Therefore, the exasperated Romans crushed them. And these left the region. Some of them were dispersed to Epirus and Macedonia, and a large number established themselves in Hellas”
From the above, we can see that the Byzantine chronicler knew about the Vlachs as the same same as the Dacians who lived in the vicinity of the River Sava where it flows into the Danube (modern day Vojvodina Serbia) who had been dispersed from there into the Empire. For a brief reminder of the audience, the ancient Dacians lived in the modern day Romania, which was called as Dacia The approximate territorial distribution of various Dacian tribes is depicted below
Who were those Dacians / Vlachs that Kekaumenos was referring to? It is very possible that the author was referring to Carpian people who kept attacking the Empire until late 3rd century. A 15th century copy of the Cosmographia by Claudi Ptolemei places the Carpi people north of the Carpathian mountains
According to Ammianus Marcellinus some of the Carpi had been deported to Pannonia Inferior in 300AD, and lived there for a long time. Interesting thing is that any Byzantine chronicler remembered about the Carpi people that late, like 700 hundred years later.
On could suspect that the Vlachs/Dacians moved to the Empire in the 4th century, but then the question is how come they never rebelled ever since given they very nasty character? I suspect that those Vlachs move to Thessalia (Hellas) one or two generations prior to the chronicler, just in time to cause troubles worthy of mentioning