From the patristic age until the Gregorian calendar reform of
1582, computus – the science of time reckoning and art of
calendar construction – was a subject of intense concern to
medieval people. Bede’s The Reckoning of Time (De temporum
ratione) was the first comprehensive treatise on this subject,
and the model and reference for all subsequent teaching,
discussion and criticism of the Christian calendar. The
Reckoning of Time is a systematic exposition of the Julian solar
calendar and the Paschal table of Dionysius Exiguus, with their
related formulae for calculating dates. But it is more than a
technical handbook. Bede sets calendar lore within a broad
scientific framework and a coherent Christian concept of time,
and incorporates themes as diverse as the theory of tides and
the threat of chiliasm. This translation of the full text
includes an extensive historical introduction and a chapter-by-
chapter commentary. The Reckoning of Time also serves as an
accessible introduction to the computus itself.