In This Article Expand or collapse the "in this article" section Calendars and Time (Christian)

  • Introduction
  • Computus and Chronology: The 11th and 12th Centuries
  • Mentalities of Time-Reckoning

Medieval Studies Calendars and Time (Christian)
Faith Wallis
  • LAST REVIEWED: 13 January 2014
  • LAST MODIFIED: 13 January 2014
  • DOI: 10.1093/obo/9780195396584-0130


Medieval people differentiated days according to their position within the week, their date in the Roman solar calendar, and their associated religious commemorations. Marking times by these criteria was the business of computus (“computation,” specifically computation of time), the body of data, precept, and technique required to manage the Christian calendar, and in particular, to determine the calendar date of Easter. As many liturgical commemorations within the year were scheduled in relation to Easter, this date had to be established well in advance. Paschal tables thus required some form of prospective era such as annus Domini or annus mundi that could be extended indefinitely, and whose year-designations were unique. Consequently, there is considerable overlap between computus and chronology. The records for both sciences are largely textual: didactic, polemical, or critical writings, graphic documents such as Paschal tables and liturgical calendars, as well as annals. But many computus treatises that aspired to be comprehensive included some discussion of hours, and these smaller units played a role in the calculations underpinning computus. The scholarship on these issues differs from that on computus and chronology in its focus on measuring instruments (sundials, clocks, etc.). Computus tended to attract into its orbit mathematics, astronomy, and other scientific topics required for time-reckoning, or for which time-reckoning was required (e.g., medicine). These subjects, save when they connect directly with computus, are outside our scope, as are the philosophy and theology of time in general. Nonetheless, the growing scholarship on how time- reckoning reflected and influenced medieval religious and social culture will be considered. The chronological limits of this essay extend from the Patristic period, when Christian computus and chronology took shape, up to the reform mandated by Pope Gregory XIII in 1582. In that year, the dates from 5 to 14 October were cancelled to restore congruence between the calendar dates for the solstices and equinoxes, and astronomical reality. Other adjustments were made to prevent future discrepancies between lunar and solar phenomena and to secure the correct determination of Easter. The Gregorian reform was thus significant for computus, though not for chronology or the measurement of diurnal time. The geographical scope is Latin Christendom, but the Patristic background encompasses the ancient Roman Empire.

Surveys and Reference Works

Medievalists seek information about time reckoning to study the phenomenon of time-reckoning itself, or to decipher and verify temporal references in medieval sources. Reference manuals and general surveys often attempt to answer both purposes.

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