In subsequent times, however, when regular historical annals began to be recorded, chronologists attempted to reason backward, from events whose periods were known, through various data which they ingeniously obtained from the preceding and less formal narratives, until they obtained the dates of earlier events by a species of calculation. In this way the time for the building of Rome was determined to be about the year 754 before Christ. As to Romulus himself, the tradition is that he was but eighteen or twenty years old when he commenced the building of it. If this is true, his extreme youth goes far to palliate some of the wrongs which he perpetrated--wrongs which would have been far more inexcusable if committed with the deliberate purpose of middle life, than if prompted by the unthinking impulses and passions of eighteen. A certain Roman philosopher, named Varro, who lived some centuries after the building of the city, conceived of a very ingenious plan for discovering the year in which Romulus was born. It was this. By means of the science of astrology, as practiced in those days, certain learned magicians used to predict what the life and fortunes of any man would be, from the aspects and phases of the planets and other heavenly bodies at the time of his birth. The idea of Varro was to reverse this process in the case of Romulus; that is, to deduce from the known facts of his history what must have been the relative situations of the planets and stars when he came into the world! He accordingly applied to a noted astrologer to work out the problem for him. Given, a history of the incidents and events occurring to the man in his progress through life; required, the exact condition of the skies when the child was born. In other words, the astrologer was to determine what must have been the relative positions of the sun, moon, and stars, at the birth of Romulus, in order to produce a being whose life should exhibit such transactions and events as those which appeared in Romulus's subsequent history. When the astrologer had thus ascertained the condition of the skies at the time in question, the _astronomers_, as Varro concluded, could easily calculate the month and the year when the combination must have occurred.