Seeing Chrsmat71's cleaned AE3 of Valentinian I, the "Gloria Romanorum" - dragging a "Barbarian" captive, and recalling a previous "Smackdown" on Emperors with their foot on a "Barbarian" made me think about the increasing depiction of the western Emperors being depicted on their coins subduing or with their foot on a "Barbarian" and how it seemed to tally with the increase in the real power "Barbarians" had in the western Empire.
I noticed that in the gold coinage of the late Western empire, the emperor was depicted with his foot on the head of a Barbarian.
http://wildwinds.com/coins/ric/vale...RIC_2010.txtThis type is described as a "Human Headed Serpent".
(There may well be some Christian symbolism, using a Serpent as an "evil emblem", ironic when we recall the "pagan" Salus types were the snake was revered.)
That "Human Headed Serpent" might be just a decapited head of a long haired "Barbarian" such as a Burgundian, of which it is well known they wore their hair long.

Depiction of a Gallo-Roman landlord handing over his property rights to a Burgundian warlord.
The irony was, that it was these "Barbarians" whose feet began to make their impact on the "head" of the western Roman empire, making and breaking "emperors" who became mere puppets, a trend which continued unabated until the forced abdication of Romulus "Augustulus" in 476 AD.
Julius Nepos, a rival western emperor, held out in the province of Dalmatia until 480 AD, when he was killed by his own army, which is likely to have mostly consisted of "Barbarians".
Then Syagrius, the last
Magister Militum of Gaul, overthrown by the Franks, fled south to the Visigoths, then sent back north to the Franks and then assassinated by order of the Frankish king in 486 AD.
But I have not seen any "Barbarian" coins with the king depicted with his foot on the head of a Roman, but then the Roman civilians outnumbered the "Barbarians", seeing a coin with a depiction of one of them beheaded, under the foot of a "barbarian" king would have caused a rebellion.
So we see the propaganda power that coins have, and for the "Barbarians", using coinage to show them as the continuators of "Romanitas" was just as an effective weapon in the subduing and control of the former Roman provinces as any levies they could muster.