Rome’s wall begun in 378 B.C. took twenty-five years to build. However secure she might feel behind it, immediately beyond the gates lurked enemies. To the north the Gauls, to the east and south, Italic tribes (whom Rome successively feared, rivalled, dominated, and invited to partnership; of these the Samnites were the most fearsome), on the seas the Syracusan and Carthaginian navies--all represented a clear and present danger. Rome’s population being inadequate to keep legions in the field, much less a fleet at sea, against all these threats at once, she evolved a system of advanced bases, called Latin colonies (Fig. 4.1), manned partly with trustworthy local non-Romans, though with a hard core of Roman legionaries. This avoided undue drain on the Roman manpower, and placed the responsibility for frontier defense upon frontiersmen who had the greatest interest in their own security. During the last thirty years the efforts of archaeologists of several nations; for example, Italians at Ostia, Belgians at Alba Fucens, Americans at Cosa have added much to the sum of our knowledge of these frontier outposts: their fortifications, street plan, public buildings, housing arrangements, and the surveyed (“centuriated”) quarter-sections of land (allotments) stretching away from the walls into the countryside round about. From these brute facts inferences can be drawn, about what prompted the founding of these outposts (was the motive always military?), about relations with neighbors and with Rome, about communications, about economic, social, and cultural life. [Illustration: FIG. 4.1 Roman colonization. (P. MacKendrick, _Archaeology_ 9 [1955], p. 127)]