While Prescott was still engaged in his Mexican and Peruvian researches, and, in fact, even before he had undertaken them, another fascinating subject had found lodgement in his mind. So far back as 1838, only a few months after the publication of _Ferdinand and Isabella_, he had said: "Should I succeed in my present collections, who knows what facilities I may find for making one relative to Philip the Second's reign--a fruitful theme if discussed under all its relations, civil and literary as well as military." And again, in 1839, he reverted to the same subject in his memoranda. Could he have been sure of obtaining access to the manuscript and other sources, he might at that time have chosen this theme in preference to the story of the Mexican conquest. He knew, however, that nothing could be done unless he were able to make a free use of the Spanish archives preserved at Simancas. To this ancient town, at the suggestion of Cardinal Ximenes, the most precious historical documents relating to Spanish history had been removed, in 1536, by order of Charles V. The old castle of the Admiral of Castile had been prepared to receive them, and there they still remained, as they do to-day, filling some fifty large rooms and contained in some eighty thousand packages. It has been estimated that fully thirty million separate documents of various kinds are included in this remarkably rich collection,--not only state papers of a formal character, but private letters, secret reports, and the confidential correspondence of Spanish ambassadors in foreign countries.[17] Such a treasure-house of historical information scarcely exists elsewhere; and Prescott, therefore, wrote to his friends in Madrid to learn whether he might hope for access to this Spanish Vatican. In 1839, however, he made the following memorandum: "By advices from Madrid this week, I learn that the archives of Simancas are in so disorderly a state that it is next to impossible to gather material for the reign of Philip II." His friend, Arthur Middleton, cited to him the instance of a young scholar who had been permitted to explore these collections for six months, and who had found that the documents of a date prior to the year 1700 were "all thrown together without order or index." Furthermore, Prescott's agent in Spain, Dr. Lembke, had incurred the displeasure of the government, which expelled him from the country. Prescott was, therefore, obliged for the time to put aside the project of a history of Philip II., and he turned instead to the study of the Mexican conquest.