The irregularity of the lengths of the months descends from the
Roman calendar, which came to be adopted throughout Europe and then worldwide. The months of Rome's original
lunar calendar would have varied between 29 and 30 days, depending on observations of the
phases of the moon. Reforms credited to
Romulus and
Numa established a set year of twelve fixed months. Possibly under the influence of the
Pythagoreans in southern Italy, Rome considered odd numbers more lucky and set the lengths of the new months to 29 and 31 days, apart from the last month
February and the
intercalary month Mercedonius. which was known to consist of of 1461 days (rather than 1460 days) by the time of
Meton in the 5thcenturyBC. Rather than adopt a new system like the
Egyptian calendar, which had 12 months of 30 days each and a set, annual intercalary month of 5 days,
Caesar aimed for
his 46BC reform to maintain as much continuity as possible with the old calendar. Ultimately, Mercedonius was removed, the four existing 31-day months were maintained, February was left unchanged apart from leap years, and the needed additional ten days of the year were added to the 29-day months to make them either 30 or 31 days long. By the
Renaissance, the irregularity of the resulting system had inspired
Latin verses to remember the order of long and short months. The first known published form appeared in a 1488 edition of the Latin verses of
Anianus: In 2011, the Welsh author Roger Bryan discovered an older English form of the poem written at the bottom of a page of
saints' days for February within a Latin manuscript in the
British Library's
Harleian manuscripts. He dated the entry to 1425 ±20 years. The first published English version as "A Rule to Know How Many Dayes Euery Moneth in the Yere Hath": "September" and "November" have identical rhythm and rhyme and are thus poetically interchangeable. It is less common now and September variants have a long history as well. A manuscript copy of the verse from runs: An alternate version of this verse, published in 1827, runs: Another version, published in 1844, runs: Another English version from before 1574 is found in a manuscript among the Mostyn Papers held at the
National Library of Wales in
Aberystwyth. Variants appear throughout Europe. The typical Italian form is: ==Legacy==