Today (23 September) is the birthday of Augustus Caesar, and yesterday was the birthday of Bilbo and Frodo Baggins. So it is entirely meet, fitting, and proper to write about a little known parallel between the Rome and the Shire.
cum aliquos numquam soluturos significare uult, 'ad K(a)l(endas) Graecas soluturos' ait.
When [Augustus] wished to indicate that some people would never pay their debts, he said that they would pay them 'on the Greek Kalends.'
Suetonius, Augustus, 87.1
The first day of every Roman month was known as 'the Kalends' of that month (hence our 'calendar'). Since Greeks did not use the Roman calendar, there could be no 'Greek Kalends'.
Meanwhile in the Shire the first day of a non-existent month also gave rise to a joke:
It will be noted if one glances at a Shire Calendar, that the only weekday on which no month began was Friday. It thus became a jesting idiom in the Shire to speak of 'on Friday the first' when referring to a day that did not exist. or to a day on which very unlikely events such as the flying of pigs or (in the Shire) the walking of trees might occur. In full the expression was 'on Friday the first of Summerfilth'.
(RK App. D 1109 n. 2)
The month 'Summerfilth' does not exist. It is a play on 'Winterfilth', which is roughly equivalent with October, a name Tolkien derived, Winterfylleþ, the first month of Winter among the Anglo-Saxons.