Civilizations may last for centuries and be extremely eventful; Imperial Rome is a prime example.
But autumn ends, and a civilization becomes a culture gone frozen in its brains and heart, and its finale is anything but grand. We are now far into what the Chinese called the period of contending states, and the collapse of Caesarism.
In such a period, politics becomes an arena of competing generals and plutocrats, under a dummy ruler chosen for low intelligence and complete moral plasticity, who amuses himself and keeps the masses distracted from their troubles with bread, circuses, and brushfire-wars. (This is the time of all times when a culture should unite — and the time when such a thing has become impossible.) Technology flourishes (the late Romans were first-class engineers) but science disintegrates into a welter of competing, grandiosely trivial hypotheses which supersede each other almost weekly and veer more and more markedly toward the occult.
Among the masses there arises a "second religiousness" in which nobody actually believes; an attempt is made to buttress this by syncretism, the wrenching out of context of religious forms from other cultures, such as the Indian, without the faintest hope of knowing what they mean. This process, too, leads inevitably towards a revival of the occult, and here science and religion overlap, to the benefit of neither. Economic inequity, instability and wretchedness become endemic on a hitherto unprecedented scale; the highest buildings ever erected by the Classical culture were the tenements of the Imperial Roman slums, crammed to bursting point with freed and runaway slaves, bankrupts, and deposed petty kings and other political refugees.From Probapossible Prolegomena to Ideareal History by James Blish (1978) (quoted at Atomic Rockets) (underline added).