According to the later writers Censorinus and Macrobius, the ideal intercalary cycle consisted of ordinary years of 355 days alternating with intercalary years, alternately 377 and 378 days long.
12.
Macrobius describes a further refinement whereby, in one 8-year period within a 24-year cycle, there were only three intercalary years, each of 377 days ( thus 11 intercalary years out of 24 ).
13.
Macrobius describes a further refinement whereby, in one 8-year period within a 24-year cycle, there were only three intercalary years, each of 377 days ( thus 11 intercalary years out of 24 ).
14.
The known examples of such dates are all after the Ides of February, which suggests they are connected with resolving an ambiguity that could arise in intercalary years : dates of the form " a . d . [ N ] Kal.
15.
Macrobius describes a further refinement whereby, in one 8-year period within a 24-year cycle, there were only three intercalary years, each of 377 days . This refinement brings the calendar back in line with the seasons, and averages the length of the year to 365.25 days over 24 years.
16.
This followed naturally, because the days after the Ides ( 13th ) of February ( in an ordinary year ) or the Ides of Intercalaris ( in an intercalary year ) both counted down to the Kalends of March ( i . e . they were known as " the " n " th day before the Kalends of March " ).
17.
In intercalary years, the first part of February was terminated on the 23rd, i . e ., the day of the " Terminalia ", and the festivals normally held in the last five days of February were held instead in the last five days of the intercalary month, immediately before the " Kalends " of March.
18.
In the Macedonian period ( 307 / 306 224 / 223 BC ), with twelve tribes ( and the prytanies ), evidence shows that the month and the prytany were not coterminous and that, in general, the six first prytanies had 30 days and the last six had 29 days and that in an intercalary year, the 384 days are equally subdivided . ( Meritt, 1961 : Ch . VI)
19.
In the Thirteen Phylai period ( 224 / 223 201 / 200 BC ), it would be expected that in an intercalary year prytanies and months must have been fairly evenly matched and that in an ordinary year, the conciliar year was made up of three prytanies of 28 days followed by ten prytanies of 27 days, but there is strong evidence that the first prytany had usually 27 days . ( Meritt, 1961 : Ch . VII)
20.
Some scholars, such as Ludwig Ideler, Henry G Liddell, the staff writers of " Encyclopaedia Britannica " and Elias Bickerman hold that in intercalary years February's length was fixed at 23 days and it was followed by a variable length " mensis intercalaris " with 27 or 28 days . This view is followed in generalist surveys of calendrical history such as those of D E Duncan, G R Richards or A Aveni.
