This extent and harmony of design is unquestionably that which distinguishes the work of Gibbon from all other great historical compositions. He has first bridged the abyss between ancient and modern times, and connected together the two great worlds of history. The great advantage which the classical historians possess over those of modern times is in unity of plan, of course greatly facilitated by the narrower sphere to which their researches were confined. Except Herodotus, the great historians of Greece—we exclude the more modern compilers, like Diodorus Siculus—limited themselves to a single period, or at least to the contracted sphere of Grecian affairs. As far as the _Barbarians_ trespassed within the Grecian boundary, or were necessarily mingled up with Grecian politics, they were admitted into the pale of Grecian history; but to Thucydides and to Xenophon, excepting in the Persian inroad of the latter, Greece was the world. Natural unity confined their narrative almost to chronological order, the episodes were of rare occurrence and extremely brief. To the Roman historians the course was equally clear and defined. Rome was their centre of unity; and the uniformity with which the circle of the Roman dominion spread around, the regularity with which their civil polity expanded, forced, as it were, upon the Roman historian that plan which Polybius announces as the subject of his history, the means and the manner by which the whole world became subject to the Roman sway. How different the complicated politics of the European kingdoms! Every national history, to be complete, must, in a certain sense, be the history of Europe; there is no knowing to how remote a quarter it may be necessary to trace our most domestic events; from a country, how apparently disconnected, may originate the impulse which gives its direction to the whole course of affairs. In imitation of his classical models, Gibbon places _Rome_ as the cardinal point from which his inquiries diverge, and to which they bear constant reference; yet how immeasurable the space over which those inquiries range! how complicated, how confused, how apparently inextricable the causes which tend to the decline of the Roman empire! how countless the nations which swarm forth, in mingling and indistinct hordes, constantly changing the geographical limits—incessantly confounding the natural boundaries! At first sight, the whole period, the whole state of the world, seems to offer no more secure footing to an historical adventurer than the chaos of Milton—to be in a state of irreclaimable disorder, best described in the language of the poet:—