By the later middle ages, Durham Priory had evolved a complex administrative structure, as befitted a leading Benedictine house of considerable wealth and influence with important temporal and secular roles. There were a number of administrative departments, each presided over by a monk (an obedientiary) who was usually assisted by other brethren in the house, lay and ecclesiastical. Eleven of these offices (or obediences) had a greater importance than the others, simply because they had wider responsibilities and so dealt with a larger annual budget. The obedientiaries holding these offices had a duty to account for their income and expenditure at the annual chapter held in June and to draw up annual statements of their finances. However, even within this group of eleven obediences some had far weightier duties than others, most notably the bursar's office, which was involved in the financial management of the prior's household as well as that of the whole monastic community and so its operations affected all the other obediences. Changes in the number and names of these offices occurred throughout the medieval period; some offices were amalgamated from time to time and held by one monk, as, for example, the offices of terrar and hostillar in the fifteenth century.