Suda (Σουδα or alternatively Suidas) is the name of a massive medieval lexicon, not an author as was formerly supposed. (The derivation is from Latin, meaning "fortress" or "stronghold".) It is an encyclopaedia with 30,000 entries, many drawing from ancient sources that have since been lost.

Little is known of the compilation of this work, except that it must have been before Eustathius (12th-13th century), who frequently quotes it. Under the heading "Adam" the author of the lexicon (which a prefatory note states to be "by Suidas") gives a brief chronology of the world, ending with the death of the emperor John Zimisces (975), and under Constantinople his successors Basil II and Constantine VIII are mentioned.

It would thus appear that the Suda was compiled in the latter part of the 10th century. The passages in which Michael Psellus (end of the 11th century) is referred to are considered later interpolations. The lexicon is arranged alphabetically with some slight deviations, letters and combinations of letters having the same sound being placed together. It thus partakes of the nature of both a dictionary and an encyclopaedia.

It includes numerous quotations from ancient writers; the scholiasts on Aristophanes, Homer, Sophocles and Thucydides are also much used. The biographical notices, the author tells us, are condensed from the Onomatologion or Pinax of Hesychius of Miletus; other sources were the excerpts of Constantine Porphyrogenitus, the chronicle of Georgius Monachus, the biographies of Diogenes Laërtius and the works of Athenaeus and Philostratus.

The work deals with biblical as well as pagan subjects, from which it is inferred that the writer was a Christian. A prefatory note gives a list of dictionaries from which the lexical portion was compiled, together with the names of their authors. Although the work is uncritical and probably much interpolated, and the value of the articles is very unequal, it contains much information on ancient history and life.

The Suda was critically edited by the Danish scholar Ada Adler (Leipzig, 1928-1938). An on-line (http://www.stoa.org/sol/) edition of the Adler edition with translations and commentary is available.

This article incorporates text from the public domain 1911 Encyclopædia Britannica.