In the polished stone age, the county had been self-supporting, because of its possession of flint. In the bronze age it was dependent upon other places, through its non-possession of copper or tin. During the former period it may have exported weapons from Cissbury; during the latter, it must have imported the material of weapons from Cornwall and Gaul. Before the Romans came, the Celts of Britain had learned the use of iron. Whether they ever worked the iron of the Weald, however, is uncertain. But as the ores lie near the surface, as wood (to be made into charcoal) for the smelting was abundant, and as these two facts caused the Weald iron to be extensively employed in later times, it is probable that small clearings would be made in the most accessible spots, and that rude ironworks would be established. The same geographical causes which made Britain part of the Roman world naturally affected Sussex, as one of its component portions. Even under the Empire, however, the county remained singularly separate. The Romans built two strong fortresses at Anderida and Regnum, Pevensey and Chichester, to guard the two Gwents or lowland plains, where the shore shelves slowly to seaward; and they ran one of their great roads across the coastwise tract, from Dover to the Portus Magnus (now Porchester), near Portsmouth; but they left Sussex otherwise very much to its own devices. We know that the Regni were still permitted to keep their native chief, who probably exercised over his tribesmen somewhat the same subordinate authority which a Rajput raja now exercises under the British government. Here, again, we see the natural result of the isolation of Sussex. The Romans ruled directly in the open plains of the Yorkshire Ouse and the Thames, as we ourselves rule in the Bengal Delta, the Doab, and the Punjab; but they left a measure of independence to the native princes of south Wales, of Sussex, and of Cornwall, as we ourselves do to the native rulers in the deserts of Rajputana, the inaccessible mountains of Nipal, and the aboriginal hill districts of Central India.