The Roman dating system continued to be used throughout the Middle Ages. Late, in the twelfth century, in the North (particularly in Germany and Norman holdings), a new system began to appear: namely, numbering the days of the month from 1 to the last day of the month (28/ 29/ 30/ 31), the practice we still follow today (dies mensis). This practice only slowly caught on, while many educated still used the previous Roman system of date reference. Let see the structure of the Roman dating system: Romans used a complex system based on three certain days (landmarks) of a month, which were operating as points of reference for the remaining days. These certain days were called Kalends (Kalendae), Nones (Nonae), Ides (Eidus). Roman months just before the Julius Caesar reform had the following names and durations: Ianuarius (29), Februarius (28), Martius (31), Aprilis (29), Maius (31), Iunius (29), Quintilis (31), Sextilis (29), September (29), October (31), November (29), December (29). Sum of days: 355. After the reform, in the years of Emperor August the months took their final names and durations, used until now: January/ Ianuarius (31), February/ Februarius (28/29), March/ Martius (31), April/ Aprilis (30), May/ Maius (31), June/ Iunius (30), Julius/ Iulius (31), August/ Augustus (31), September (30), October (31), November (30), December (31). Sum of days: 365/366. Kalends coincided with the 1st day of the month. Nones coincided with the 7th day and Ides with the 15th day of the month for the 31-days long old Roman months (Martius, Maius, Quintilis/ Julius and October) and the 5th and 13th day for the remaining months. Roman dates were counted inclusively forward to the next one of the above mentioned principal days (Kalends, Nones Ides). One should count the number of the days that include the day under examination, the next principal day and the days between. Things to be taken into account: Days before (ante diem) or the day before (pridie) the Kalends/ Nones/ Ides are written as ante diem/ pridie [the number] Kalendas/ Nonas/ Idus followed in Latin by the feminine accusative plural of the month (Ianuarias, Februarias, Martias, Apriles, Maias, Iunias, Quintiles/ Iulias, Sextiles/ Augustas, Septembres, Octobres, Novembres, Decembres) Days coincident with the Kalends or the Nones or the Ides are written as Kalendis/ Nonis/ Idibus followed by the feminine ablative plural of the month (Ianuariis, Februariis, Martiis, Aprilibus, Maiis, Iuniis, Quintilibus/ Iuliis, Sextilibus/ Augustis, Septembribus, Octobribus, Novembribus, Decembribus) Examples: 3rd of January: the 3rd day before the Nones of January (ante diem III Nonas Ianuarias) 8th of March: the 8th day before the Ides of March (ante diem VIII Idus Martias) 15th of March: Ides of March (Idibus Martiis), the date of the death of Caesar in 44 BC. 4th of April: the day just before the Nones of April (pridie Nonas Apriles) 5th of April: Nones of April (nonis Aprilibus) 1st of July: Kalends of July (Kalendis Quintilibus/ Iuliis) 19th of July: 14 days before the Kalends of August (ante diem XIV Kalendas Sextiles/ Augustas) 25th of December: 8 days before the Kalends of January (ante diem VIII Kalendas Ianuarias) In the leap year the 24th of February was repeated. According to the above system, 24th of February is ‘ante diem sextum Kalendas Martias’. So the extra day was called ‘ante diem bis sextum Kalendas Martias’, that is ‘the double sixth day before the Kalends of March’. This is the origin of the official naming of a leap year as bis-sextile year or annee bissextile (in French). Later for convenience, in the ‘dies mensis’ system, the extra date was put after the 28th of February, as 29th of February. Dionysius Exiguus (470-544), the monk who introduced the Anno Domini system for counting the years, was still using the Roman dating system. He defined the Easter Sunday of 532 AD as ‘3 Ides of April’ that is 11th of April, the Easter Sunday of 533 AD as ‘6 Kalends of April’ that is 26th of March, the Easter Sunday of 534 AD as ’16 Kalends of May’ that is 16th of April. Venerable Bede (672-735) and Charlemagne (742-814), the founder of the Holy Roman Empire, were the first who embraced and disseminated the current dating system of ‘dies mensis’.