Etymologiae (or Origines, standard abbrev. Orig.) is an encyclopedia compiled by Isidore of Seville (died 636) towards the end of his life. It forms a bridge between a condensed epitome of classical learning at the close of Late Antiquity and the inheritance received, in large part through Isidore's work, by the early Middle Ages. According to the prefatory letters, the work was composed at the urging of his friend Braulio, Bishop of Saragossa, to whom Isidore, at the end of his life, sent his codex inemendatus ("unedited book"), which seems to have begun circulating before Braulio was able to revise it, and issue it, with a dedication to the late Visigothic King Sisebut. Partly as a consequence, three families of texts have been distinguished, including a "compressed" text with many omissions, and an expanded text with interpolations.
Etymologiae presents in abbreviated form much of that part of the learning of antiquity that Christians thought worth preserving. Etymologies, often very learned and far-fetched, a favorite trope of antiquity, form the subject of just one of the encyclopedia's twenty books, but perceived linguistic similarities permeate the work. Isidore's vast encyclopedia systematizing ancient learning includes subjects from theology to furniture and provided a rich source of classical lore and learning for medieval writers.
In all, Isidore quotes from 154 authors, both Christian and pagan. Many of the Christian authors he read in the originals; of the pagans, many he consulted in contemporary compilations. Bishop Braulio, to whom Isidore dedicated it and sent it for correction, divided it into its twenty books.
- Book I: de grammatica; Trivium: grammar
- Book II: de rhetorica et dialectica; Trivium: rhetoric and dialectic
- Book III: de mathematica; Quadrivium: mathematics, geometry, music, astronomy
- Book IV: de medicina; medicine
- Book V: de legibus et temporibus; law and chronology
- Book VI: de libris et officiis ecclesiasticis; Ecclesiastical books and offices
- Book VII: de deo, angelis et sanctis; God, angels and saints: hierarchies of heaven and earth
- Book VIII: de ecclesia et sectis; The Roman Catholic Church and Jews and heretical sects, philosophers (pagans), prophets and sibyls
- Book IX: de linguis, gentibus, regnis, militia, civibus, affinitatibus; Languages, peoples, kingdoms, cities and titles
- Book X: de vocabulis; Etymologies
- Book XI: de homines et portentis; Mankind, portents and transformations
- Book XII: de animalibus; Beasts and birds
- Book XIII: de mundo et partibus; The physical world, atoms, elements, natural phenomena
- Book XIV: de terra et partibus; Geography: Earth, Asia, Europe, Libya, islands, promontories, mountains, caves
- Book XV: de aedificiis et agris; Public buildings, public works, roads
- Book XVI: de lapidibus et metallis; Metals and stones
- Book XVII: de rebus rusticis; Agriculture
- Book XVIII: de bello et ludis; Terms of war, games, jurisprudence
- Book XIX: de navibus, aedificiis et vestibus; Ships, houses and clothes
- Book XX: de domo et instrumentis domesticis; Food, tools and furnishings
"An editor's enthusiasm is soon chilled by the discovery that Isidore's book is really a mosaic of pieces borrowed from previous writers, sacred and profane, often their 'ipsa verba' without alteration," W. M. Lindsay noted in 1911, having recently edited Isidore for the Clarendon Press, with the further observation, however, that a portion of the texts quoted have otherwise been lost: the Prata of Suetonius can only be reconstructed from Isidore's excerpts. In the second book, dealing with dialectic and rhetoric, Isidore is heavily indebted to translations from the Greek by Boethius, and in treating logic, Cassiodorus, who provided the gist of Isidore's treatment of arithmetic in Book III. Caelius Aurelianus contributes generously to that part of the fourth book which deals with medicine. Isidore's view of Roman law in the fifth book is viewed through the lens of the Visigothic compendiary called the Breviary of Alaric, which was based on the Code of Theodosius, which Isidore never saw. Through Isidore's condensed paraphrase a third-hand memory of Roman law passed to the Early Middle Ages. Lactantius is the author most extensively quoted in the eleventh book, concerning man. The twelfth, thirteenth, and fourteenth books are largely based on the writings of Pliny and Solinus; whilst the lost Prata of Suetonius, which can be partly pieced together from its quoted passages in Etymolgiae, seems to have inspired the general plan of the "Etymologiae", as well as many of its details.
Through the Middle Ages Etymologiae was the textbook most in use, regarded so highly as a repository of classical learning that, in a great measure, it superseded the use of the individual works of the classics themselves, full texts of which were no longer copied and thus were lost. The book was not only one of the most popular compendia in medieval libraries but was printed in at least ten editions between 1470 and 1530, showing Isidore's continued popularity in the Renaissance, rivalling Vincent of Beauvais.
A stylized T and O map featuring the world as a wheel appeared in an early printed edition, published at Augsburg, 1472. The editio princeps, the first printed edition, was printed by Johann Sensenschmidt in Nuremberg in 1470. The continent Asia is peopled by descendants of Sem or Shem, Africa by descendants of Ham and Europe by descendants of Japheth, the sons of Noah.
 The shape of the Earth
Some writers think Isidore taught in the Etymologiae that the Earth was round "resembl[ing] a wheel". This is the same description used by the early Greek philosopher Anaximander for the sun before any spherical ideas emerged. Though, some writers believe he referred to a disc-shaped Earth, other writers believe that he considered the Earth to be a globe. He did not admit the possibility of people dwelling at the antipodes, considering them as legendary and noting that there was no evidence for their existence. Isidore's round map, also called T and O map or simply (T-O) map, continued to be used through the Middle Ages by authors such as the 9th-century bishop Rabanus Maurus who compared the habitable part of the northern hemisphere (Aristotle's northern temperate clime) with a wheel. However, "About, 1,100 maps of the earth from the eighth through the fifteenth century survive; they are almost all flat - as are maps in a modern atlas...The common circular maps called "T in O" (T-O) show the T-shaped oikoumene surrounded by the O-shaped sea. One could interpret these maps as a flat wheel or disc, but most were intended to represent only a portion of the sphere - known world - just as a modern flat map of Europe or Africa is intended to represent only part of the planet" and "In the ancient and medieval world the term "antipodes" may mean lands on the opposite side on the planet or, more commonly, "human inhabitants" of lands on the other side of the planet. Several varieties of views on the antipodes existed, some placing them in the southern hemisphere, others in the northern sphere opposite the known world. To distinguish, it will help to call the inhabitants "antipodeans".
In Book III in one section Isidore states "At the same time [the sun] rises it appears equally to a person in the east as a person in the west", implying that it is flat. But for north and south he follows works such as the Topographia Christiana saying the earth is raised up towards the northern region and declines to the south. Sysebut used the word globus meaning a sphere, in a letter to Isidore, but Isidore used the word orbis, generally meaning circle or disk. However, Isidore's understanding of the earth as a sphere can be seen in Book III Section XXXII and Book XIV Section I. Isidore states that the sphere of the sky has earth in its center and the sky being equally distant on all sides. Furthermore, in Chapter 28 of De Natura Rerum which is an earlier work used to add to sections in the "Etymologies", Isidore claims that the sun orbits the earth and illuminates the other side when it is night on this side.
Lyons says "His teachings were followed so slavishly that his assertion...that the earth was flat and 'resembles a wheel' long retained a hold on many in medieval Europe, even if a handful of scholars and learned monks knew otherwise". However, Jeffrey Burton Russell in his review of the formation of the Flat Earth myth, which was invented in the past two centuries, argues that there were sufficient lines of evidence and widespread acceptance among academics from the times of the early church from notable figures like Augustine of the spherical earth. The overwhelming influence of Aristotle and Ptolemy through the medieval times should not be underestimated. Russell states "The Scholastics - later medieval philosophers, theologians, and scientists - were helped by the Arabic translators and commentaries, but they hardly needed to struggle against a flat-earth legacy from the early middle ages (500-1050). Early medieval writers often had fuzzy and imprecise impressions of both Ptolemy and Aristotle and relied more on Pliny, but they felt (with one exception), little urge to assume flatness." 
The 13th-century Codex Gigas, the largest extant medieval manuscript, contains a copy of the Etymologiae. The modern critical edition, superseding W.M. Lindsay's of 1911, supervised by an International Committee of Isidorian Studies, (B. Bischoff, M.C. Díaz, J. Fontaine, J.N. Hilgarth, eds.) was announced in 1974, intended to appear in twenty volumes, one for each book, with an additional volume discussing the manuscript history and presenting a general introduction.
- The accounts of logic in Book II and of arithmetic in Book III are transferred almost word for word from Cassiodorus, Isidore's editor W. M. Lindsay observed. Lindsay, "The Editing of Isidore Etymologiae" The Classical Quarterly 5.1 (January 1911, pp. 42-53 [p 42])
- Isidori Hispalensis Episcopi Etymologiarum Sive Originum Libri XX (Oxford: Clarendon Press), 1911; see W. M. Lindsay, "The Editing of Isidore Etymologiae" The Classical Quarterly 5.1 (January 1911, pp. 42-53 (p 42).
- Lindsay 1911, eo. loc.
- Examined in detail in Johann Sofer, Lateinisches und Romanisches aus den Etymologiae des Isidorus von Sevilla, Göttingen, 1930; it was extensively criticised by Walter Porzig, "Die Rezensionen der Etymologiae des Isidorus von Sevilla." Hermes 72.2 (1937), pp. 129-170.
- Incunabula Short Title Catalogue
- Stephen A. Barney, W. J. Lewis, J. A. Beach, Oliver Berghof (translators) (2010). "XIV ii 1". The Etymologies of Isidore of Seville. Cambridge University Press.
- "The sun is a circle..like a chariot-wheel, the rim of which is hollow and full of fire. Sir Thomas L. Heath (1892). Greek Astronomy, Library of Greek Thought. London, Dent. pp. 5–7. quoted in Thomas S. Kuhn (1966). The Copernican Revolution. Harvard University Press. p. 26.
- Wesley M. Stevens, "The Figure of the Earth in Isidore's De natura rerum", Isis, 71(1980): 268-277.
- Russell, Jefrey Burton (1991). Inventing the Flat Earth: Columbus and Modern Historians. Praeger. pp. 86–87. ISBN 0-275-95904-X.
- Grant, Edward (1974). A Sourcebook in Medieval Science (Source Books in the History of the Sciences). Harvard University Press. ISBN 978-0-674-82360-0.
- Isidore, Etymologiae, XIV.v.17 TheLatinLibrary.com.
- Isidore, Etymologiae, IX.ii.133 TheLatinLibrary.com.
- Etymologies III xxx
- Epistula Sisebuti 38-41 quoted in Stevens
- Etymologies III. XXXII
- Etymologies XIV. I
- Fontaine, Jacques (1960). Isidore de Seville: Traité de la Nature. Bordeaux.
- Lyons, Jonathan (2009). The House of Wisdom. Bloomsbury. pp. 34–35.