The largest Arabic book prior to 1500 is The History of Damascus (Taʾrīkh Madīnat Dimashq, hereafter, TMD), written by Ibn ʿAsākir (d. 571/1176). Totalling over eight million words, it consists of two volumes, treating the history and religious significance of the city and Syria, followed by 72 volumes treating the biographies of the elites who lived in or passed through the region up to Ibn ʿAsākir’s time. How, in premodern times, did he compose such a massive book? What were his sources? An argument has been advanced that he relied upon a library, and its contents are proposed based chiefly on isnāds and citations within the TMD itself. The paper relies on a new data set to propose a different understanding of the source base of the TMD and indeed, the character of the book itself. The first element of the data set is 77,000 isnāds extracted from the book, plus the names he cites (including authors) and the terms by which he cites them. A second element is from search results across the TMD, including for titles and author names. The final element is text reuse alignments between the TMD and 37 books which scholars today say Ibn ʿAsākir used to compile the TMD and for which we have machine-readable files. We use this data to argue that the character of his source base is better represented by notes, excerpts and compilations (e.g., various lists, including those that start with the term tasmiya) than by books sitting on the shelf of a library. Indeed, he rarely cites books, even those we can see he used. Rather, Ibn ʿAsākir spells out what he is doing, thousands of times: relying on many connections and numerous personal relationships running back decades and spanning a vast geography. He assembles pieces of reporting for the TMD from this network, and indeed, would memorialise through the isnāds the community of scholars that it represents. He wants to show us these personal relationships, including their connections back in time to the Prophet. We conclude with a description of the many other works by Ibn ʿAsākir that focus on isnāds and which likely provided material for the TMD, including those that are lost and in an unpublished manuscript. These also help us to understand how he worked and more about the character of the TMD itself.