Sardinia has been inhabited since prehistoric times. The primary evidence of the proto-Sardic people and culture are the nuraghi, ancient, conical-shaped stone dwellings, of which about 6,500 have been identified; little else is known about these original Sardinians. The Phoenicians, mainly interested in trade, established peaceful contacts with the Sardinians around 1000 B.C. They were followed by the Carthaginians during the sixth century B.C. , who warred with the Sardinians and conquered much of the island, as did the Romans from 238 B.C. ; these two periods of domination were militarily, Economically, and politically quite similar. The changes imposed by these powers have influenced the development of the Island ever since. Interested only in exploiting the fertile plains and mineral-rich hills, the invaders conquered and occupied only the lowland areas, where latifundist estates and mines were established. The indigenous peoples either were subjugated or sought refuge in the highlands, which the Romans called "the land of the barbarians," the region known as Barbagia today. Thus Sardinia was divided into two socioEconomic subregions: the foreign-dominated agricultural Lowlands and the independent but impoverished agropastoral highlands; this separation has characterized Sardinia until present times. The Vandals conquered Sardinia in A.D. 455, but throughout their eighty-year domination they, too, failed to penetrate the mountain refuge areas. Sardinia became a province of Byzantium in A.D. 534; by the eighth century, However, the authorities began gradually to withdraw, ushering in a period of autonomous government, an indigenous renaissance based on communal landholdings and administration by local assemblies of freemen. The absence of a strong military power on the island was a temptation to both the pirates and the pope: Pisa and Genoa allied with the Sardinians to oust the Arabs, staying on to compete among themselves for dominance. From 1323 to 1478, Aragon fought for control of the island, initiating four centuries of Spanish domination. Spanish feudalism was essentially parasitic, feeding an absentee aristocracy, which led to economic isolation and stagnation in Sardinia; Spanish exploitation primarily took the form of taxation, which left communities relatively free to organize production according to traditional forms. Thus, the subsistence-oriented economies based on agriculture in the Lowlands and pastoralism in the highlands persisted in Sardinia much longer than in the rest of Europe, and the island became more and more of an underdeveloped backwater. In the nineteenth century, Sardinia passed to Savoy under treaty, and was incorporated into the Italian state with unification in 1860. The greatest changes in Sardinian society have been since World War II, as the Italian state has instituted policies to stimulate development and modernization throughout the mezzogiorno (southern Italy).