At Mortlake, in the house by the Thames, Dee assembled what was probably the largest library in England: his own catalogue of 1583 lists around three thousand printed books and a large collection of manuscripts, at a time when the college libraries of Oxford and Cambridge held far less. It was a working national resource before England had one.
Scholars, navigators and courtiers came to consult the books and the man who had read them; Dee had petitioned Mary's government in 1556 for a royal library that would gather the scattered monastic manuscripts, was refused, and then built privately what he had proposed publicly. The collection's fate is the dark half of the story.
When Dee left for the continent in 1583 with Edward Kelley, he entrusted the house to his brother in law; in his absence the library was plundered, books sold and instruments broken, and though he recovered part of it on his return, he spent his last years selling volumes to eat. The dispersal seeded other collections, and Mortlake books, identifiable by his tidy annotations, surface today in the British Library, the Bodleian and the Royal College of Physicians, which holds the largest single group. His marginalia have become a field of study in themselves: a record of how the most learned man of Elizabethan England actually read, annotating navigation and number, angels and chronology, with the same pen.