The Suda or Souda (ˈsuːdə; Soûda; Suidae Lexicon) is a large 10th-century Byzantine encyclopedia of the ancient Mediterranean world, formerly attributed to an author called Soudas (Σούδας) or Souidas (Σουίδας). It is an encyclopedic lexicon, written in Greek, with 30,000 entries, many drawing from ancient sources that have since been lost, and often derived from medieval Christian compilers. The derivation is probably from the Byzantine Greek word souda, meaning "fortress" or "stronghold", with the alternate name, Suidas, stemming from an error made by Eustathius, who mistook the title for the author's name. Paul Maas once ironized by suggesting that the title may be connected to the Latin verb suda, the second-person singular imperative of sudāre, meaning "to sweat", but Franz Dölger traced its origins back to Byzantine military lexicon (σοῦδα, "ditch, trench", then "fortress"). Silvio Giuseppe Mercati, on the other hand, suggested a link with the Neo-Latin substantive guida ("guide"), transliterated in Greek as γουίδα. A more recent theory by Carlo Maria Mazzucchi (Catholic University of the Sacred Heart, Milan) sees the composition of the encyclopedia as a collective work, probably in a school. During the process, the entries (from more than 40 sources) were written down on file cards collected in a fitting receptacle before they were transcribed on quires. That happened before 970, and further entries were then added in the margins. Mazzucchi explains the name Σοῦδα (meaning "ditch") as both an acrostic of Συναγωγὴ ὁνομάτων ὑπὸ διαφόρων ἁρμοσθεῖσα ("Collection of nouns assembled from different [sources]") and a memory of the receptacle that used to contain the file cards. Most likely, the name is the acronym ΣΟΥΙΔΑ = ΣΥΝΤΑΞΙΣ ΟΝΟΜΑΣΤΙΚΗΣ ΥΛΗΣ ΙΔΙΑ ΑΛΦΑΒΗΤΙΚΗΣ (ΣΕΙΡΑΣ): Composition of Named Subjects in (by) Alphabetical (Order). It is clearly stated upfront: ΤΟ ΜΕΝ ΠΑΡΟΝ ΒΙΒΛΙΟΝ, ΣΟYΙΔΑ. ΟΙ ΔΕ ΣΥΝΤΑΞΑΜΕΝΟΙ ΤΟΥΤΟ ΑΝΔΡΕΣ ΣΟΦΟΙ. (THE PRESENT BOOK, SOYΙDA. THOSE THAT COMPOSED IT WISE MEN).