But as a knowledge of topography is necessary for the right understanding of my narrative, I must state the places from which Hannibal started, through which he marched, and into which he descended when he arrived in Italy. Nor must I, like some historians, content myself with mentioning the mere names of places and rivers, under the idea that that is quite sufficient to give a clear knowledge. My opinion is that, in the case of well-known places, the mention of names is of great assistance, but that, in the case of unknown countries, names are no better than unintelligible and unmeaning sounds: for the understanding having nothing to go upon, and being unable by referring to something known to translate the words into thought, the narrative becomes confused and vague, and conveys no clear idea. A plan therefore must be discovered, whereby it shall be possible, while speaking of unknown countries, to convey real and intelligible notions. The first, most important, and most general conception is that of the division of the heaven into four quarters, which all of us that are capable of a general idea at all know as east, west, south, and north. The next is to arrange the several parts of the globe according to these points, and always to refer in thought any place mentioned to one or other of them. We shall thus get an intelligible and familiar conception of places which we do not know or have never seen.