The average length of a period of civilisation is 1330 years. Ours Petrie dates from about A.D. 450. It has always needed a fresh race to produce a new period of civilisation. In Europe, between A.D. 300 and 600, some fifteen new races broke in from north and east for slow mixture. “If,” he concluded, “the source of every civilisation has lain in race mixture, it may be that eugenics will, in some future civilisation, carefully segregate fine races, and prohibit continual mixture, until they have a distinct type, which will start a new civilisation when transplanted. The future progress of Man may depend as much on isolation to establish a type as on fusion of types when established.” At the time when Flinders Petrie was publishing his suggestive book, Dr. Oswald Spengler, apparently in complete ignorance of it, was engaged in a far more elaborate work, not actually published till after the War, in which an analogous conception of the growth and decay of civilisations was put forward in a more philosophic way, perhaps more debatable on account of the complex detail in which the conception was worked out.[123] Petrie had considered the matter in a summary empiric manner with close reference to the actual forces viewed broadly. Spengler’s manner is narrower, more subjective, and more metaphysical. He distinguishes—though he also recognises eight periods—between “culture” and “civilisation.” It is the first that is really vital and profitable; a “civilisation” is the decaying later stage of a “culture,” its inevitable fate. Herein it reaches its climax. “Civilisations are the most externalised and artistic conditions of which the higher embodiment of Man is capable. They are a spiritual senility, an end which with inner necessity is reached again and again.”[124] The transition from “culture” to “civilisation” in ancient times took place, Spengler holds, in the fourth century, and in the modern West in the nineteenth. But, like Petrie, though more implicitly, he recognises the prominent place of the art activities in the whole process, and he explicitly emphasises the interesting way in which those activities which are generally regarded as of the nature of art are interwoven with others not so generally regarded. III HOWEVER we look at it, we see that Man, whether he works individually or collectively, may conveniently be regarded, in the comprehensive sense, as an artist, a bad artist, maybe, for the most part, but still an artist. His civilisation—if that is the term we choose to apply to the total sum of his group activities—is always an art, or a complex of arts. It is an art that is to be measured, or left immeasurable. That question, we have seen, we may best leave open. Another question that might be put is easy to deal with more summarily: What is Art?