Smart ancient people

[LeBrok]

How come ancient Phoenicians/Carthaginians, Greeks and Romans were so smart? At least at the beginning and the height of their times. Basically they invented and laid down all the building blocks of sciences, literature, arts, architecture, finances etc. And we are talking about a million of citizens in each country, not 50 million as right now.
High national average IQ?
Smart elite?
Pure luck?

Then when their civilizations collapsed, there was a big mess in Europe. The rest of European peoples couldn't grow or even continue on Romans and Greeks achievements, and Europe went into dark ages for next 1 000 years. Why was that? Was the rest of Europe no smart enough? Low average HQ?
One could assume that through disasters/bottle necks of middle ages they did smarten up finally.

[Maciamo]

I don't think they were smarter than average, and certainly not smarter than smart people today. Great achievements have more to do with political stability, good economy, and a favourable cultural setting. The main reason Europe fell unto the Dark Ages is Christianity. The Dark Ages didn't start after the fall of the Roman Empire, but in the 4th century when Christianity became the state religion. The Byzantines remained independent for a thousand years after the fall of Rome, but were just a bleak shadow of the pre-Christian Roman Empire.

Christianity made people wait for a better after-life paradise instead of trying to improve society. It strongly discouraged sciences, innovations and any philosophical questioning of how Nature works. Furthermore the Church acted as an absolute monarchy of divine right, and encouraged a feudal system in which the European aristocracy was subjugated to the Pope's will. The Roman Catholic Church saw itself as the heir of the Roman Empire. It was like a virus taking over a healthy body and turning it into a zombie.

Europe managed to extricate itself from the grip of the Church little by little from the 15th to the 18th century. Once educated people stopped being Christian a new era of progress was born, known as the Enlightenment. Our modern society was basically founded by the 18th-century Enlightenment (except for some religious zealots who couldn't stand it and migrated to America, notably in the south-eastern US states where the Enlightenment still hasn't reached most of the population).

People have been smart for thousands of years. It's just that they are not always free to use their potential because of oppressive religions. The two most intellectually oppressive religions in history are Christianity and Islam.