When the principle of mutual support was hit upon, and the arch sprang self-balanced from impost to impost, the Roman was put in possession of an immense advantage over the restricted capacities of the Greek entablature. He was no longer tied to the width or length of quarried blocks, put in vertical or horizontal positions, but could bend more pliant materials in yet firmer construction upward and outward to an illimitable extent. In its use they soon became the best builders the world had ever seen, and the worst architects. The magnitude of their great works, and boldness of execution, the vastness of design and mechanical skill, displayed in their existing monuments, compel us to admire the constructive talent of Rome, as Greece taught us to revere inventive genius. Unyielding energy and graceful elegance are brought into striking contrast. On the one hand, we behold the same iron greatness, indomitable will, and union of physical with moral vigor, combined with indifference to intellectual beauty, which bent alike the material and political world beneath the yoke of old Rome. On the other hand, in the Grecian temple shines the purest product of mind, perfect in symmetry, chaste in ornament, and resplendent with all the attractions of immortal youth. The best and only satisfactory works of the Romans are those we usually classify under the head of engineering; such as roads, bridges, aqueducts, and fortifications, and these are projected on a scale, and executed with a solidity, worthy of the greatness of their empire. But in architecture properly so called, nothing of their creation is to be admired but the colossal mass, and its constructive extravagance.