rulers: Navarre, Aragon (a kingdom by 1035), and, on the Mediterranean coast, the Catalan districts, expanding under the leadership of the counts of Barcelona. The first gains were made as the men of the Asturias and Galicia pushed southwards to the River Duero. By 1085 the Castilians had reached the Tagus and by the beginning of the twelfth century the Aragonese and Catalans were consolidating their power in the Ebro valley.

In this early period, where nothing so definite as a fixed frontier between Christian and Muslim territory can be envisaged, power was based on the taking of strongholds and the exaction of tribute from the fragmented Muslim powers which had succeeded the great caliphate of Cordoba. The taifa, or 'party kings' fought amongst themselves in the south and were easy prey for the working of what has aptly been described as a 'protection racket system' run by the neighbouring Christian powers. This involved the payment of parias, fixed cash sums in return for military help against their Muslim rivals. The parias provided an essential part of the regular income of the Christian rulers; Alfonso VI exacted payments from ' Abd Allah, ruler of Granada, amounting to 30,000 dinars down and a further 10,000 dinars annually.

The successful working of this system of profitable extortion was dependent on two factors: the inability of the Muslim princelings to form lasting alliances amongst themselves and the consolidation of territorial gains by the Christian forces. The existence of a Christian settler population, which moved into areas freed from the threat of Muslim attack, provided the necessary infrastructure to survive any Muslim counter-attack. The tenth-century northern migration of Mozarabs (Arabized Christians) and the subsequent encouragement of colonists from north of the Pyrenees, provided a settler population which could consolidate the successes of the Christian raiding parties. Their presence in often dangerous regions was encouraged by the Spanish monarchs and this chiefly explains the prevalence of freeholdings in the countryside and the granting of town customs (fueros or cartas pueblas) which gave their populations a high degree of autonomy. In many areas, small or

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