had common characteristics. They appear to have been in what the geographers usually delineate as tropical savannah, humid sub-tropical, tropical and sub- tropical steppes or sometimes deserts, with periodic wet seasons and a rainfall of at least 10 but not over 30 inches a year. Moreover, the frontier campaign area was generally grassy with deciduous trees or desert. In relative terms the frontier was not heavily populated, but adjoined on such an area. It was a marginal re- gion for cultivation, a beef or cattle country, often a sheep one, but never a swine-herding space (except in the Balkans and Manchuria). Obviously some major frontier areas, such as those of the northern Roman Empire, Siberia, Can- ada and Australia do not fit into this description. But Australia, at least, has a history almost devoid of internal military action. At this point the commonality of geographical features has yet to be studied in depth. It is not possible to evaluate its significance in the same way that the belt of battlefields in Flanders, for instance, can be analysed. It can only be suggested that these areas seem to lend themselves to agriculture and economic exploitation and that they were open for military activity - the type of country in which officers with agrarian backgrounds, if not urban ones, liked to operate and forage.
Much that happened and still happens on the frontiers is only comprehen- sible when the peoples on each side are understood. National characteristics, density of population, resources and opportunities, as well as climate molded the approach. Thus, the West in the United States, unlike its contiguous counterpart in Canada, had neither the aristocratic British officers and their code of conduct nor the smartly uniformed troops nor yet the Royal Canadian Mounted Police, all of which may be summed up as an extension of the hard-to-define national self-image, of which British officers and NCO's made their men conscious. The U.S. frontier seems, then, brash, the Canadian restrained. One has the feeling that the same applied to Caesar's legions also. The moving spirit was a righteous crusade to bring civilization and its camp-followers to the natives, along with other things. On any of these frontiers - whether of the first century B.C. or of the 19th A.D. is immaterial - preparing the local residents for the "modern world" would remain part of the frontier military mission until either the evacua- tion of the last post (whether that retreat took place for political, military, diplo- matic, economic, social or ideological reasons) or merely that the frontier had moved on.
Military frontiers went forward usually through a series of posts, but the speed of advance varied with the interest of the government, the menace to the settlers, if any, and the character of the commander at the moment.
The military usually fought their strongest frontier campaign in an open area better suited than natural frontiers for major campaigns. It was, too, a place in which herds of grazing animals - cattle, sheep, horses or buffalo - represented a form of movable wealth. And perhaps a reason for the longevity of this type of campaign was the enjoyable nature of the contest for the encroaching power. In