Editing Leap year (section)

===Early Roman practice===
{{further|Julian calendar#Motivation}}
The early [[Roman calendar]] was a lunisolar one that consisted of 12&nbsp;months, for a total of 355&nbsp;days. In addition, a 27- or 28-day [[intercalary month]], the {{lang|la|[[Mercedonius|Mensis Intercalaris]]}}, was sometimes inserted into February, at the first or second day after the {{lang|la|[[Terminus (mythology)|Terminalia]]}} {{lang|la|a. d. VII Kal. Mar.}} (23 February), to resynchronise the lunar and solar cycles. The remaining days of Februarius were discarded. This intercalary month, named {{lang|la|Intercalaris}} or {{lang|la|[[Mercedonius]]}}, contained 27&nbsp;days. The religious festivals that were normally celebrated in the last five&nbsp;days of February were moved to the last five&nbsp;days of Intercalaris. The lunisolar calendar was abandoned about 450&nbsp;BC by the {{lang|la|[[decemviri]]}},<ref>According to [[Christian Ludwig Ideler]] (1825)</ref> who implemented the [[Roman calendar|Roman Republican calendar]], used until 46&nbsp;BC. The days of these calendars were counted down (inclusively) to the next named day, so 24 February was {{lang|la|ante diem sextum Kalendas Martias}} ["the sixth day before the calends of March"] often abbreviated {{lang|la|a. d. VI Kal. Mart.}} [[Ancient Rome|The Romans]] counted days inclusively in their calendars, so this was the fifth day before 1 March when counted in the modern exclusive manner (i.e., not including both the starting and ending day).<ref name=Key>{{citation |first = Thomas Hewitt |last = Key |url=https://penelope.uchicago.edu/Thayer/E/Roman/Texts/secondary/SMIGRA*/Calendarium.html |title=Calendarium |publisher=University of Chicago| orig-year = 1875 |date=2013 |quote=the intermediate days are in all cases reckoned backward upon the Roman principle already explained of counting both extremes.}}</ref> Because only 22 or 23&nbsp;days were effectively added, not a full [[lunation]], the calends and ides of the Roman Republican calendar were no longer associated with the new moon and full moon.{{citation needed|date=February 2024}}