Inter gravissimas

Inter gravissimas (English: "Among the most serious...") was a papal bull issued by Pope Gregory XIII on 24 February 1582.

The intention expressed by the text of this bull was "to restore" the calendar so that seasonal events critical for the calculation of Easter dates would be back in their "proper places" and would be prevented from being moved away again.

The first two items were the ones that received attention; the third, about choosing the next following Sunday, was not identified as causing any problem, and was not further mentioned.

Gregory also made changes to the calendar rules, intending to ensure that, in the future, the equinox and the 14th day of the Paschal moon, and consequently Easter Sunday, would not move away again from what the bull called their proper places.

[6] The version of "Inter gravissimas" included by Christoph Clavius in his work explaining the Gregorian calendar contained these dating clauses: "Anno Incarnationis Dominicae M. D. LXXXI.

... Anno à Natiuitate Domini nostri Iesu Christi Millesimo Quingentesimo Octuagesimo secundo Indictione decima,".