Much of the confusion that ensues from the study of history is due to the fact that we take it upon ourselves to arrange the subject into those supremely annoying quantities called "centuries." As a matter of mathematical convenience, I've got nothing against centuries, though I may have a number of things against math. But as a strictly practical contrivance, the century is not without its benefits, and Gregory, Julius or whoever it was that suggested the device in the first place undoubtedly merits a slightly higher position amid the Nine Circles for having done so. At first glance, the century charms us with its neatness. Any division of time is a supreme artifice by its very nature, and the partition of epochs into quantities of a hundred is one sufficiently fascile to appease both the lazy and the choleric minded among us, which two categories probably account for the greater majority of contemporary historians.
A more attentive inspection, however, proves that history ought not be divided up into anything as neat, moderate and dismissive of events as the century; and this because history is neither neat nor moderate, and if she is dismissive, it is only of practitioners of the second quality. History is naturally imbalanced, discordant and messy. The century fails to take these marks into its accounting of her.
Consider, for example, the Gothic Era; the Fall of the Western Empire, Odoacer, the deposition of Romulus Augustulus, etc., at 476 A.D. The end of that same period, say, at the Battle of Tours, the inauguration of the Carolingian Rennaisance, 732 A.D. No clean division of centuries here, but historians nonetheless feel it devolves upon them to mark each century with a characteristic of its own, like a group of fastidious authors that pay too much attention to minor characters; the twentieth century becomes the century of spiritual ennui (a quality equally prevalent in the nineteenth) and aesthetically the era of theoretical decenteredness (appicable also to the eighty year period in English letters between Mallory and Shakespeare). The measurment of history in terms of defining events is also a pebble in the shoe of any advocate of The Century; properly speaking, the twentieth century begins in 1900, but in actuality, 1914 is a more acceptable date, as is September 11th, 2001, rather than January 1st, 2000, for the date of its expiration. Almost every preceeding "century" is beset with the same inconvenience; the 19th century, as it turns out, was actually 125 years long (1789-1914) and the century prior to that even more difficult to estimate; it begins with the end of the Thirty Years' War, and ends with the French Revolution, making it 141 years in length. The Thirty Years' War, in turn, was merely the final evolution in the religious wars which, along with uglier churches and abominable fashion developments in Puritan circles, had been the primary product of the Reformation, which all testifies to the fact that the Thirty Years War was a more truly a part of the Sixteenth Century than to the following one, ergo the century that followed didn't actually happen.
It's really quite simple if you think it over for a minute.