THE BEGINNINGS OF MEDIEVAL INFORMATION VISUALIZATION - Information Visualisation: Techniques, Usability and Evaluation - page 12

Clearly, these illustrations were an important part of musical pedagogy
that justified the investment of significant skill and effort required for their
reproduction.
Isidore of Seville
Born in Cartagena, Spain, around 560 CE, Isidore of Seville is considered
one of the greatest scholars of late antiquity, best known as the first
encyclopedist of the Middle Ages [25]. His Etymologiae ( Etymologies ) is a
wide-ranging work in twenty topics that quotes over 154 classical authors
encompassing grammar, religion, law, agriculture, medicine, and more
[26]. Etymologiae was the textbook most in use throughout the Middle
Ages, regarded so highly as a repository of classical learning that, in great
measure, it superseded the use of the individual works of the classics
themselves, full texts that were no longer copied and thus were lost.
Etymologiae and De natura rerum [27] are two of his works that are of
interest to the history of information visualization, because they contain
diagrams he considered useful for the communication of ideas. In
particular, De natura rerum contains seven figures, six of which are
circular diagrams called rotae , that Isidore employs for conveying a
variety of concepts including cartography, computus, the elements, and the
relation of man to the cosmos. Two kinds of rotae will be considered here.
Figs 1.5 and 1.6 display respectively two examples of rotae that appear
in copies of De natura rerum , the first diagram produced in the women's
cloister of Chelles on the Marne east of Paris in about the year 800 (MS
Cod. Sang. 240, fol. 124, St. Gallen, Stiftsbibliothek) [28], and the second
created between the years 760 and 780 at St. Gall (MS Cod. Sang. 238,
fol. 325, St. Gallen, Stiftsbibliothek) [29].This schema was designed to
communicate the concordance between the Roman (Julian) and Egyptian
calendars [30]. Egyptian calendars were composed of twelve 30 day
months, with five days remaining at the end of the year. Each rota serves
to convey the number of days that the start of each Egyptian month
precedes the onset of each Roman month by. Beginning at five o'clock on
the rota in Fig. 1.5, the labels of the outer ring are read clockwise as the
months January through to December, for the twelve radial divisions of the
circle. The second ring inward contains Roman numerals followed by the
letters KL , which specify the number of days that the beginning of the
Egyptian month precedes the kalends ( KL ), the first day of the Roman
month. The three inner rings may be read from the centre outward in the
following way to give the number of days in each month in the Egyptian
calendar: Roman numerals - diebus (days) - month name .