modern civilisation is in a large measure the outcome of this network of roads, and we can distinctly trace a difference in the culture of a nation where such roads never existed--as in Russia and Hungary, as contrasted with the west of Europe, where they formed the best means of communication. It was only in the neighbourhood of these highways that the fullest information was obtained of the position of towns, and the divisions of peoples; and a sketch map like the one already given, of the chief Roman roads of antiquity, gives also, as it were, a skeleton of the geographical knowledge summed up in the great work of Ptolemy. But of more importance for the future development of geographical knowledge were the great caravan routes of Asia, to which we must now turn our attention. Asia is the continent of plateaux which culminate in the Steppes of the Pamirs, appropriately called by their inhabitants "the Roof of the World." To the east of these, four great mountain ranges run, roughly, along the parallels of latitude--the Himalayas to the south, the Kuen-Iun, Thian Shan, and Altai to the north. Between the Himalayas and the Kuen-lun is the great Plateau of Tibet, which runs into a sort of cul-de-sac at its western end in Kashmir. Between the Kuen-lun and the Thian Shan we have the Gobi Steppe of Mongolia, running west of Kashgar and Yarkand; while between the Thian Shan and the Altai we have the great Kirghiz Steppe. It is clear that only two routes are possible between Eastern and Western Asia: that between the Kuen-lun and the Thian Shan via Kashgar and Bokhara, and that south of the Altai, skirting the north of the great lakes Balkash, Aral, and Caspian, to the south of Russia. The former would lead to Bassorah or Ormuz, and thence by sea, or overland, round Arabia to Alexandria; the latter and longer route would reach Europe via Constantinople. Communication between Southern Asia and Europe would mainly be by sea, along the coast of the Indies, taking advantage of the monsoons from Ceylon to Aden, and then by the Red Sea. Alexandria, Bassorah, and Ormuz would thus naturally be the chief centres of Eastern trade, while communication with the Mongols or with China would go along the two routes above mentioned, which appear to have existed during all historic time. It was by these latter routes that the Polos and the other mediæval travellers to Cathay reached that far-distant country. But, as we know from Marco Polo's travels, China could also be reached by the sea voyage; and for all practical purposes, in the late Middle Ages, when the Mongol empire broke up, and traffic through mid Asia was not secure, communication with the East was via Alexandria.