The monograph is the first study in Russia of the early medieval Irish picture of the world, which is considered in the broad context of the Celtic mythological tradition. Geographically, the monograph covers Ireland and partly Wales. The study of ancient Irish (and Middle Welsh) texts, however, is not isolated from comparative Indo-European material and other ancient mythologies and traditions: Gallic, Greek, Indian. The mythology of space, the mythology of knowledge, and the transition from traditional preliterate to written Christian culture occupy a central place in the book. The phenomenon of sacred pentads that structure the space of the island, unique to Irish mythology, is examined. The book is intended for historians, philologists and anyone interested in the culture of Celtic Europe.