[Arragonis]

Originally Posted by jamesqf

Even then, the observant realized what was happening: Plato, Critias ca 400 BC

I don't think he was writing about the same area, but it isn't clear. The full text is here, the section quoted is :

Now the country was inhabited in those days by various classes of
citizens;-there were artisans, and there were husbandmen, and there
was also a warrior class originally set apart by divine men. The
latter dwelt by themselves, and had all things suitable for nurture
and education; neither had any of them anything of their own, but they
regarded all that they had as common property; nor did they claim to
receive of the other citizens anything more than their necessary food.
And they practised all the pursuits which we yesterday described as
those of our imaginary guardians. Concerning the country the
Egyptian priests said what is not only probable but manifestly true,
that the boundaries were in those days fixed by the Isthmus, and
that in the direction of the continent they extended as far as the
heights of Cithaeron and Parnes; the boundary line came down in the
direction of the sea, having the district of Oropus on the right,
and with the river Asopus as the limit on the left. The land was the
best in the world, and was therefore able in those days to support a
vast army, raised from the surrounding people. Even the remnant of
Attica which now exists may compare with any region in the world for
the variety and excellence of its fruits and the suitableness of its
pastures to every sort of animal, which proves what I am saying; but
in those days the country was fair as now and yielded far more
abundant produce. How shall I establish my words? and what part of
it can be truly called a remnant of the land that then was? The
whole country is only a long promontory extending far into the sea
away from the rest of the continent, while the surrounding basin of
the sea is everywhere deep in the neighbourhood of the shore. Many
great deluges have taken place during the nine thousand years, for
that is the number of years which have elapsed since the time of which
I am speaking; and during all this time and through so many changes,
there has never been any considerable accumulation of the soil
coming down from the mountains, as in other places, but the earth
has fallen away all round and sunk out of sight. The consequence is,
that in comparison of what then was, there are remaining only the
bones of the wasted body, as they may be called, as in the case of
small islands, all the richer and softer parts of the soil having
fallen away, and the mere skeleton of the land being left. But in
the primitive state of the country, its mountains were high hills
covered with soil, and the plains, as they are termed by us, of
Phelleus were full of rich earth, and there was abundance of wood in
the mountains. Of this last the traces still remain, for although some
of the mountains now only afford sustenance to bees, not so very
long ago there were still to be seen roofs of timber cut from trees
growing there, which were of a size sufficient to cover the largest
houses; and there were many other high trees, cultivated by man and
bearing abundance of food for cattle. Moreover, the land reaped the
benefit of the annual rainfall, not as now losing the water which
flows off the bare earth into the sea, but, having an abundant
supply in all places, and receiving it into herself and treasuring
it up in the close clay soil, it let off into the hollows the
streams which it absorbed from the heights, providing everywhere
abundant fountains and rivers, of which there may still be observed
sacred memorials in places where fountains once existed; and this
proves the truth of what I am saying.

Oropus is in Greece just north of Athens. Attica is the region of Greece around Athens. Cithaeron (Kithairon) is in central Greece, Parnes (Parnitha) is a mountain range in Northern Greence.

The description of a bit of land sticking out into the sea and the small Islands would match the general shape of Greece and its surroundings.

The text is quite "dense", as in hard to interpret though - so this could be incorrect.