During the Medieval period, Arithmetic did not involve the study of computations, but involved the study of theories underlying the study of numbers. The Medieval curriculum for Arithmetic was based on the work of Aristotle and it incorporated some of Aristotle's philosophy regarding the relationships and ratios of numbers.
The Medieval Liberal Arts Curriculum: Arithmetic
There was also at the time a separate branch of Arithmetic which had to do ne branch of Arithmetic dealt with the mystical significance and meanings of numbers akin to what we in the modern world know of today as numerology. Some of the mystical strains of the study of numbers were derived from the scriptures or the kabala. The number three, for example, was regarded as is a number of particular significance: the three entities of the godhead; the number of days Chirst lay dead etc. Other numbers that were considered to be particularly significant were number seven and forty.
Much of the mystical branch of Arithmetic was linked also to the study of astrology which in the Middle Ages was regarded as a legitimate science.
The Medieval Curriculum