ignorabilis_; one whose existence nobody was bound to take notice of. A Persian, indeed, was allowably absent; because, as a permanent public enemy, he could not safely be present. But as to all others, and therefore as to Romans, the rule of law held--that 'to those not coming forward and those not in existence, the same line of argument applies.' [_De non apparentibus et de non existentibus eadem est ratio._] Had this been otherwise--had the two nations met freely before the light of history had strengthened into broad daylight--it is certain that the controversies upon chronology would have been far more and more intricate than they are. This profound[30] separation, therefore, has been beneficial to the student in one direction. But in another it has increased his duties; or, if not increased, at all events it serves to remind him of a separate chapter in his chronological researches. Had Rome stood in as close a relation to Greece as Persia did, one single chronology would have sufficed for both. Hardly one event in Persian history has survived for our memory, which is not taken up by the looms of Greece and interwoven with the general arras and texture of Grecian history. And from the era of the Consul Paulus Emilius, something of the same sort takes place between Greece and Rome; and in a partial sense the same result is renewed as often as the successive assaults occur of the Roman-destroying power applied to the several members of the Graeco-Macedonian Empire. But these did not commence until Rome had existed for half-a-thousand years. And through all that long period, two-thirds of the entire Roman history up to the Christian era, the two Chronologies flow absolutely apart. Consequently, because all chronology is thrown back upon Europe, and because the pre-Christian Europe is split into two collateral bodies, and because each of these separate bodies must have a separate head--it follows that chronology, as a pre-Christian chronology, will, like the Imperial eagle, be two-headed. Now this accident of chronology, on a first glance, seems but too likely to confuse and perplex the young student.