The Suda or Souda (Medieval Greek: Σοῦδα Soûda; Latin: Suidae Lexicon) is a massive 10th-century Byzantine encyclopedia of the ancient Mediterranean world, formerly attributed to an author called Suidas. It is an encyclopaedic lexicon, written in Greek, with 30,000 entries, a large number of drawing from ancient sources that have after been lost, and often derived from mediaeval 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.


The Suda is somewhere between a grammatical dictionary and an encyclopaedia in the modern sense. It explains the source, derivation, and meaning of words according to the philology of its period, using such earlier authorities as Harpocration and Helladios. The articles on literary history are especially valuable. These entries supply details and quotations from authors whose works are otherwise lost. They use older scholia to the classics (Homer, Thucydides, Sophocles, etc.), and for later writers, Polybius, Josephus, the Chronicon Paschale, George Syncellus, George Hamartolus, and so on.

This lexicon represents a convenient work of reference for persons who played a part in political, ecclesiastical, and literary history in the East down to the tenth century. The chief source for this is the encyclopaedia of Constantine VII Porphyrogenitus (912–59), and for Roman history the excerpts of John of Antioch (fifth century). Krumbacher (Byzantinische Literatur, 566) counts two main sources of the work: Constantine VII for ancient history, and Hamartolus (Georgios Monachos) for the Byzantine age.


The lexicon is arranged alphabetically with a few slight deviations from common vowel order and place in the Greek alphabet (including at each case the homophonous digraphs, e.g. αι, ει, οι, that had been previously, earlier in the history of Greek, distinct diphthongs or vowels) according to a system (formerly common in a large number of languages) called antistoichia (ἀντιστοιχία); namely the letters follow phonetically in order of sound, in the pronunciation of the tenth century which is similar to that of Modern Greek. The order is:

α, β, γ, δ, αι, ε, ζ, ει, η, ι, θ, κ, λ, μ, ν, ξ, ο, ω, π, ρ, σ, τ, οι, υ, φ, χ, ψ

In addition, double letters are treated as single for the purposes of collation (as gemination had ceased to be distinctive). The system isn't difficult to learn and remember, but a few editors—for example, Immanuel Bekker – rearranged the Suda alphabetically.


Little is known of the compilation of this work, except that it must have taken place before Eustathius who quoted frequently from it in the twelfth century. 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 I Tzimiskes (975), and the article "Constantinople" mentions his successors Basil II (976–1025) and Constantine VIII (1025–1028). It would thus appear that the Suda was compiled in the latter part of the tenth century. Passages referring to Michael Psellus (end of the eleventh century) are considered later interpolations.

It includes numerous quotations from ancient writers; the scholiasts on Aristophanes, Homer, Sophocles and Thucydides are additionally much used. The biographical notices, the author avers, are condensed from the Onomatologion or Pinax of Hesychius of Miletus; additional sources include the excerpts of Constantine Porphyrogenitus, the chronicle of Georgius Monachus, the biographies of Diogenes Laertius and the works of Athenaeus and Philostratus. Other principal sources include a lexicon by "Eudemus," perhaps derived from the work On Rhetorical Language by Eudemus of Argos.

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 its articles is quite unequal, the Suda contains much useful information on ancient history and life. Its quotations from ancient authors make it a useful cheque on their manuscript traditions. A modern translation, the Suda On Line, was completed on 21 July 2014.

The Suda has a near-contemporaneous Islamic parallel, the Kitab al-Fehrest of Ibn al-Nadim. Compare additionally the Latin Speculum Maius, authored in the thirteenth century by Vincent of Beauvais.