The "Fundamental Book of the Entire Middle Ages" (E. R. Curtius) Isidore of Seville (circa 560 - 636) is considered by some to be the last author of Latin mother tongue. His presidency at the Fourth Council of Toledo (633) influenced Spanish history - but above all, he achieved extraordinary significance through his extensive literary work. In his writings, preserved in over a thousand manuscripts, he addresses scientific, grammatical, historical, and theological topics. The main work in the series of scientific writings is the Etymologiae, written for King Sisebut in 20 books, which he completed around 630. The ambitious goal of this thematically organized encyclopedia was to explain the world and all its phenomena through the names of things. The result of the work was a concise summary of the intellectual.