:The composition of Hypaspistai and Doryphoroi (both are Buccellarii) is difficult to explain.
Even if most of them were drawn inside the empire is it fact that many goths served as Buccellarii - because they settled on roman land long time ago (thracia, Illyria, dalmatia).
So, those "Roman warriors" were probably a mixture of many nationes or tribes. Narses 400 Buccellarii were Langobardi and Huns... just an example - and this is a fact.
source: Bury, Hist. o. the late Rom. Emp.vol.2 and
Teall, The barbarians in Just. armies; Speculum 40 page 249-322.
Those pages (Teall, p249-322) are describing that the eastern Romans rarely used Soccii (Symmachoi) from outside the empire. The western empire used many of them before they felt, that's the reason why their army was finally perforated like a cheese from swizerland. The field army was based on mercs from outside the empire.
The eastern empire recruited many troops from Roman land. However, those so called "Romans" were often Heruls, Goths, Armenians (many many Armenians!), Isaurians... people who lived, settled and worked long time on Roman land. They identified themself a lot of times as Romani.
And this affects the Phoideratoi as well as the Boukelarioi.
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By the way (I found this information some minutes ago in my book from Robert Grosse): the leader of the Buccellarii of Belisar was Hildiger - he was a Goth too.