The role played by the military orders, almost always with the encouragement and support of the Holy See, in all the longstanding conflicts between Christian and Muslim powers scarcely needs highlighting. As in all prolonged wars, the antagonists were profoundly transformed, pacts and alliances were made and dissolved, and the political geography of the opposing sides underwent important modifications. Some of the most significant changes to occur came about as a consequence of the adaptation of crusading ideology to fit the realities of the twelfth-century Iberian Peninsula and the continued threat posed by the islamic states. In this setting, frontier warfare, with its widespread if spasmodic and desultory conflicts, predominated. This situation, coupled with seasonal fighting, logistical difficulties, scarcity of trained men and precarious chains of command, to mention only a few factors, called for the introduction of the military orders, which had already proved their worth in the Holy Land. Similarly, the creation of new regional militias became imperative and unavoidable. The former had to adapt to the specific characteristics of this new theatre of operations, while the latter came into being in accord with local needs, resources and demography.