The article I read was
still sticking to the idea that it was
Heraclius for the following reasons ( I understand the shaky footing of coin portraiture in late
antiquity so don't worry I'm not saying it is necessarily correct)
1) The diadem is a
type that is very uncommon on Valentinian's coins and more common on far later Imperial
portraits.
you see how the front of the diadem protrudes slightly like the diadem on the statue rather than lies flat. This is more common on later
portraits from
Tiberius II onwards.
2) The way the diadem sits is very different to the
portraits of earlier Late Antique emperors. The coins and
bust of Valentinian show the diadem fitting closely behind the ears and the ears themselves are clearly visible. The
Colossus however has the diadem worn slightly higher with the ears mostly covered by a thick
head of hair. This can be seen on several coin
types of
Heraclius.
3) The beard. Now this may seem inconsequential but I believe that Emperors were very particular in creating their public image and any feature on a statue like this is there because they wanted it. It's not a case of them just forgetting to shave before getting their statue done.
Heraclius often was portrayed with a short beard as the coin above shows.
4)
Heraclius has reason to deserve a statue like this after fighting a 6 year war against the Persians from 622-628AD
Those are the idea put forward by F.P Johnson in a very old article on the topic....now my own thoughts as to why it is not Valentinian.
The rendering of the
face is a lot simpler than the
bust of Valentinian. I would have expected for such an immense public
work as this the finest craftsmanship rather than the rather clumsy angular features on the
Colossus. This to me implies a later date to the piece.
Anyway I accept none of this makes a watertight case but that's the fun of it.