When you think of classical society, you think of Rome and Greece. While they were two of the greatest kingdoms on earth, they had many weaknesses that caused them to fall. I will examine weakness in the three biggest aspects of their lives.
The Greeks and Romans had a polytheistic pagan religion that eventually degraded into a humanistic form of thinking. Towards the end of Grecian times, most Greeks did not actively practice their religion; they used it as a means to explain things and nothing else. If something bad happened, they would say, "The gods willed it." To the Greeks and Romans, true faith was in the hands of man. Many philosophers, Socrates especially, taught that man should be a good citizen and do good works through the power of him. Socrates strongly believed in the concept of man the thinker, man the doer, and man the maker. The problem in that is the Greeks believed that the city-state was the world, so they thought that the betterment of mankind was in the betterment of the city-state. So the Greeks were caught up in the analysis part of doing that their society made little progress. The case was different with Rome, they were men of action, and they put the Greek's thoughts into action. The problem of this was, it was abused. Roman political leaders squandered and misused all that the Romans did. It was all wasted in petty wars, greedy dealings, and many other things that led to the Roman's downfall. .
The Greeks and Romans had very little common moral grounds. The mainstream thinking was serve the city-state, life a good life, and have fun. The Greeks had no standard ethics system, other than don't betray the city-state. What led to the downfall of Greco-Roman morals is the fact that there were no laws governing them. Their religion did not have an ethics system as Christianity does. .
Greco-Roman society had no ethics base, no formal religion, and no stable government.