Gerbert of  Aurillac, Brother Adam, medieval astronomy, medieval geography,timekeeping, horology

This paper focuses on the letter, written by Gerbert of  Aurillac (Pope Sylvester II) in  the late 980s, which was addressed to brother Adam who is otherwise unknown to us from other sources. Gerbert's text deals with the  problems of  timekeeping and  it naturally uses professional astronomical and geographical terminology and concepts which were necessary for timekeeping during this period. Although our contemporary knowledge of brother Adam is lacking, this paper sets out to analyse the letter and to reconstruct the individual fragments of teachings which had to be available to the recipient of the letter (i.e. brother Adam). This paper thus focuses on some topics of the medieval (inspired by antiquity) geocentric view of the organization of the Cosmos together with the basic categories of geographical division of the Earth and, at the same time, the paper is trying to draw attention to the fact that such concepts could have been the part of elementary knowledge of an educated individual by the end of 10th century.