Three-Tier System of Administration for Military Orders
In the years immediately following foundation, a [Christian] military order [like the Knights Templar] consisted of a small group of brethren under the leadership of a master. At this stage little governmental machinery was needed. As property and recruits were gained, it became the norm to establish subordinate convents, both in frontier regions and elsewhere. If expansion was considerable, an intermediate tier of government between convents and the order’s headquarters was soon needed, as it became difficult for masters to supervise distant convents. Also, a system was needed by which resources and recruits could easily be channelled to frontier regions from other convents. Orders which fought on several fronts also required a military leader in each district. They adopted the practice of grouping the convents of a region into what were called provinces or priories. Although there were variations in detail, the leading orders adopted a three-tier system of administration.
— Jonathan Riley-Smith (editor), The Oxford Illustrated History of the Crusades, p. 204
