The most famous work of the “first encyclopedist of the Middle Ages,” Isidore, Bishop of Seville (c. 570–636), is a comprehensive system of human knowledge that became a link between the spiritual world of antiquity and subsequent eras. The translation offered to the reader of the first three of the twenty books covers the field of science, which in medieval universities was usually called “the seven liberal arts,” and is an ancient textbook on Latin grammar, rhetoric, logic, arithmetic, geometry, music theory and astronomy. For the first time for the Russian-speaking reader, these disciplines are presented as they were seen by teachers and students in the Middle Ages. The author compiled his books based on materials from ancient science, and even more broadly, from the entire cultural universe of antiquity, systematizing, classifying and transforming it for educational purposes. The publication is intended for a wide range of readers interested in the spiritual culture of antiquity and the Middle Ages, and is equipped with an article, notes and indexes.