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Gregory XIII reforms the calendar

1582 · Rome (Rome, Italy)

In February 1582 Gregory XIII's bull Inter gravissimas reforms the Julian calendar, removing ten days that October and correcting the leap year rule. Catholic states adopt the Gregorian calendar at once; Protestant and Orthodox lands follow over the following centuries, and it becomes the civil calendar of the world.

Tagged: Catholic

The Event

Date
1582 (exact)
Era
Reformation and Counter-Reformation; Standard periodization of Catholic history
Location
Rome; today Rome, Italy
Traditions
Catholicism
Streams
Catholic
Key figures
Gregory XIII, Christopher Clavius
Key texts
Inter gravissimas

Connections

Illustration for Council of Trent History Event Council of Trent 1545–1563 completes the calendar correction the council requested

Primary Sources

  • Gregory XIII, Inter gravissimas, 1582.

Secondary Sources

  • Chadwick, Owen. A History of the Popes, 1830-1914. Oxford: Clarendon Press, 1998.
  • Duffy, Eamon. Saints and Sinners: A History of the Popes. New Haven: Yale University Press, 2006.
  • Hastings, Adrian, ed. A World History of Christianity. Grand Rapids: Eerdmans, 1999.
  • MacCulloch, Diarmaid. A History of Christianity: The First Three Thousand Years. London: Penguin, 2009.
  • O'Malley, John W. Trent: What Happened at the Council. Cambridge, MA: Harvard University Press, 2013.

Provenance: HIST-1332; confidence 0.95; accessed 2026-10-30.

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