A feature of imperial Rome was the “annona”, the distribution of free bread to the plebs. This naturally created a large but idle population, and created servility out of a free people. “Free stuff” tends to do that. It is remarkable that, when Constantinople was created, the emperor decided to institute a similar system there. The population of Constantinople duly increased. The grain to fund this came from Egypt. It is interesting that even in the (medieval) Life of St Nicholas, there is a memory of requisitioned ships from Alexandria, bearing grain for the capital.
But when did this free distribution stop?
The answer may be found in the Chronicon Paschale, which has the following entry in the reign of Heraclius for 618 AD (taken from the TTH translation, p.164):
618. Indiction 6, year 8, the 7th post-consulship of Heraclius Augustus.
And from 22nd inclusive of the month January it is recorded as year 6 of the reign of Heraclius II Constantine.
In this year the recipients of the state bread were requested for 3 coins (nomismata) for each loaf as a levy. And after everyone had provided this, straightway in the month August of the same indiction 6 the provision of this state bread was completely suspended.
As far as I know there is no subsequent mention of the “state bread”.
In this, as in so much, the reign of Heraclius marks the end of the Roman period and the beginning of the medieval Greek state. The Greeks still continued to call themselves “Romans”, but it was a very different world.
Heraclius had little choice in the matter. At this time Egypt was under Persian control. There was no grain to be had. It is a nice touch, tho, that he charged every recipient a fee. Doubtless they paid, expecting it to be a one-off levy. Doubtless the emperor already knew that the distribution would not continue.