century when these pressures had been removed. It did so with differing intensity in different regions and occurred here earlier and there later because the dynamic was essentially local; the lord who consolidated and developed his powers obliged his neighbours to do likewise if they preferred not to be drawn into his lordship, but equally the lord who was less active in these respects gave much smaller reason to his neighbours to construct and intensify their own lordships. Local pressures were also accentuated by technological developments in war, and by the varying degree to which different lords or entire regions might adapt to the greatly increased costs which these developments brought in their train.

Wars might be fought for plunder or for conquest. In the former case the essential elements for the attacker were surprise and mobility, while the effective response for the defender was to keep wealth in well-fortified and well-garrisoned places. In the latter case the attacker needed an army strong enough to deal with the forces which would be led against it or to make its escape if those forces proved too great, but his principal aim was to waste the countryside. Campaigns were generally limited to the months immediately before harvest, though southern regions, dependant upon viticulture, fruit, or olives were vulnerable throughout the year. The requirements for this means of waging war were sufficient speed to launch an attack, intercept one, or evade an interception, and sufficient protection and training to destroy an inferior force or hold off a superior one. These requirements were best met in the mounted knight; protective mail armour and shield, a horse bred to bear the weight of a man so equipped, a high saddle and stirrups which enabled the rider to put his horse's momentum behind his spearpoint, and the lengthy training which gave him the skill to control these elements and to act in concert with his fellows made the knight the dominant force in battle. Knights were never the most numerous element in any army--they were too expensive for that--but they did represent the element which could force a battle by its mobility and win it by its strength. Describing the French knights who passed through Constantinople in 1097, the Greek historian Anna Comnena

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