To judge of the practical reasonableness of a style of building, it is not enough to prove that it answers its purpose; we may pre-suppose that all civilised people would effect as much as that--indeed, that all people would do so who can construct at all; for if uncivilised, their aim would be more simple and more readily attained. The question is, whether the purpose is provided for by means consistent with common sense, with the laws of nature, with the properties of the materials at hand, and without an expenditure of labour and material disproportioned to the result. In this I do not restrict the question to merely utilitarian results, but admit the artistic element in a degree proportioned to the rank and purpose of the edifice. I would also wish to guard myself against being understood to imply that the superior reasonableness of a style of architecture proves a higher state of civilisation among the people who use it. Inventions are often accidental, and independent of high civilisation. Thus, though an arch is a more rational means of spanning a wide opening than a single block of marble, the early Romans who used the arch were probably much less civilised than the early Greeks, who were ignorant of it. The Egyptians and the Greeks used most nobly the means of spanning openings with which they were best acquainted, and for which their numerous quarries of granite and marble supplied them so liberally with the materials; but such a mode of construction is manifestly costly, dependent upon natural facilities of the most exceptional kind, and extremely limited in its application. The use of the arch obviates all these difficulties, and consequently a mode of construction which admits the arch is more rational than one which does not. Roman architecture, in short, than Greek. The Romans were, in fact, eminently a practical race, and their architecture is in its construction in a high degree practical and rational; they by no means limited themselves to the use of costly and bulky materials, but united in their structures the use of all the materials of which their world-wide dominion gave them command, and were equally successful in employing in them the most stupendous masses of marble, as at Baalbec, the granite of Egypt, or the flint-nodules of Kent; and never hesitated at spanning the widest structure with vaults of domes of such solidity as almost to defy the ravages of the elements and of time.