In late medieval Sicily, the 'conservator' and the 'magistri rationales' conducted two separate but intertwined reviews of the accounts annually produced by the various monetary officers operating in the fragmented financial administration of the island. Whereas the control exercised by the 'magna curia rationum' followed the traditional procedure based on the audit of the accounts at the end of the administrative year, the conservator introduced an innovative revision practice that continued into the modern era. Through thorough inspection of the financial records, the 'conservatoria'’s staff were able to verify if the actual revenues and expenditures of the various officers in charge of collecting and delivering moneys and goods on behalf of the Crown were consistent with the budget that had been produced at the beginning of the year. The monitoring activity of the 'conservator' was possible thanks to the development since 1414 of an ingenious information management technology that combined bookkeeping and record-keeping methods. The material result of this intellectual development was the creation of a system through which the 'conservatoria'’s staff could organise an unprecedented amount of information, including any privilege, letter, decree, or any other documentation concerning the royal patrimony of the kingdom of Sicily into a book system of series and subseries dedicated to various specific financial matters. Among the various book series of the 'conservator', the so-called books of the accounts stand out as its most significant tools of administrative and financial knowledge. In essence, these books allowed the 'conservatoria'’s staff to produce annual accounts parallel to those officially prepared by the treasurer and the other principal financial officers of the realm. This system of information management gave the authorities – the Aragonese monarchs and the Sicilian viceroys on their behalf – the unique opportunity to collect detailed knowledge of the financial condition of the kingdom, even before the 'magistri rationales' conducted their formal auditing after the conclusion of the administrative year. In a composite polity such as the late medieval Crown of Aragon, whose territories were scattered across the Western Mediterranean, the many series of books of the 'conservator' thus resulted in a formidable governmental tool through which the monarchs could exercise their authority from afar on one of their dominions: the kingdom of Sicily. This vast financial and bureaucratic knowledge proved crucial for allocating the revenues and expenditures of the island according to the monarchs’ needs, in essence for supporting the expensive campaign for the conquest of Naples and the later Aragonese wars in Italy and in the Mediterranean basin.