I'll quote a bit from the book, Cities in Civilization (1998), by Sir Peter Hall. This is a pretty hefty tome in which he examines a number of urban centers throughout history which he believes have, at one point in time, reached a "golden age", and tries to explain why they occurred.

Firstly, when Ancient Greece is described as a "golden age", mostly it is 5th century Periclean Athens which is being conjured.

" The crucial point about Athens is that it was first. And first in no small sense: first in so many of the things that have mattered, ever since, to western civilization and its meaning. Athens in the 5th century B.C. gave us democracy, in a form as pure as we are likely to see; in some respects, a good deal purer than has been achieved anywhere else afterwards. It gave us philosophy, including political philosophy, in a form so rounded, so complete, that hardly anyone added anything of moment to it for well over a millennium. It gave us the world's first systematic written history. It systematized medical and scientific knowledge, and for the first time began to base them on generalizations from empirical observation. It gave us first lyric poetry and then comedy and tragedy, all again so completely at an extraordinary pitch of sophistication and maturity, such that they might have been germinating under the Greek sun for hundreds of years. It left us the first naturalistic art; for the first time, human beings caught and registered for ever the breath of a wind, the quality of a smile. It single-handedly invented the principles and the norms of architecture, which all its western practioners have learned and followed (even where they were consciously rejecting them) for the next twenty-five centuries. These achievements have formed the central part of European life in all the centuries since.

"But these were not just individual happenings; they formed a whole, and the whole was both unique and extraordinary. Democracy could have happened only in a place in which people had confidence in their own independent judgements and therefore demanded the right to control their own destinies. Thinkers like Protagoras, Hippocrates, Socrates, Plato and Aristotle worked in an atmosphere of critical debate, in which they must convince a free and thinking people. There was a demand for democracy, for critical thought, which brought forth its own supply. Likewise, the dramatists could not function without their mass audience, or the sculptors without their viewers; they needed, and they got, one of the best-informed, sophisticated and sensitive audiences in history. And it all happened cumulatively; one achievement stimulated another.

"Perhaps most astonishingly, they flowered in a minute part of the earth's surface ... 'The reader is asked, for the moment, to accept this as a reasonable statement of fact, that in a part of the world that had for centuries been civilized, and quite highly civilized, there gradually emerged a people, not very numerous, not very powerful, not very well organized, who had a totally new conception of what human life was for, and showed for the first time what the human mind was for.'

"The comic poet Lysippus said ... 'If you haven't seem Athens, you're a blockhead; if you have seen it and are not struck, you're an ass; if you're pleased to go away, you're a pack horse.'"