But when their labours are viewed as regards the practice of the art, their merits are presented under a far different aspect. Whether the magnitude, the utility, the varied combinations, or the novel and important evidences of their knowledge, be considered, the Romans, in their practical works, are yet unrivalled. They here created their own models, while they have remained examples to their successors. Though not the inventors of the arch, they, of all the nations of antiquity, first discovered and boldly applied its powers; nor is there one dignified principle in its use which they have not elicited. Rivers are spanned; the sea itself, as at Ancona, is thus enclosed within the cincture of masonry; nay, streams were heaved into air, and, borne aloft through entire provinces, poured into the capital their floods of freshness, and health. The self-balanced dome, extending a marble firmament over head, the proudest boast of modern skill, has yet its prototype and its superior in the Pantheon-- Relic of nobler days and noblest arts! Despoil'd, yet perfect, with thy circle spreads A holiness appealing to all hearts-- To art a model. The same stupendous and enduring character pervaded all the efforts of Roman art, even in those instances where more ancient principles only were brought into action. Where the Greeks were forced to call the operations of nature in aid of the weakness of art, availing themselves of some hollow mountain side for the erection of places of public resort, the imperial masters of Rome caused such mountains to be reared of masonry, within their capital, for the Theatre, Amphitheatre, and Circus. Of these vast structures, where assembled multitudes might sit uncrowded, the Colosseum--the mightiest indeed, yet only one of the labours of the reign in which it was raised--contains more solid material, brought too from far, and exquisitely wrought, than all the works of either Louis XIV., or the Czar Peter--the two greatest builders among the sovereigns of modern times: From its mass, Walls, palaces, half cities, have been rear'd; Yet oft the enormous skeleton ye pass, And marvel where the spoil could have appear'd.