Today is the first day of Saturnalia, the Roman winter festival which lasted from 17-23rd December. In honour of the day, I thought that I would collect what the 5th century writer Macrobius has to say about the date, in book 1 of his book, Saturnalia. I have added additional paragraphing, to make it easier to read online.
Chap.10 …  Our ancestors restricted the Saturnalia to a single day, the fourteenth before the Kalends of January [=19th December], but, after Gaius Caesar had added two days to December, the day on which the festival was held became the sixteenth before the Kalends of January [=17th Dec.], with the result that, since the exact day was not commonly known — some observing the addition which Caesar had made to the calendar and others following the old usage — the festival came to be regarded as lasting for more days than one.
And yet in fact among the men of old time there were some who supposed that the Saturnalia lasted for seven days (if one may use the word “suppose” of something which has the support of competent authorities); for Novius, that excellent writer of Atellan plays, says: “Long awaited they come, the seven days of the Saturnalia”; and Mummius too, who, after Novius and Pomponius, restored the long-neglected Atellan to favor, says: “Of the many excellent institutions of our ancestors this is the best-that they made the seven days of the Saturnalia begin when the weather is coldest”.
 Mallius, however, says that the men who, as I have already related, had found protection in the name of Saturn and in the awe which he inspired, ordained a three-day festival in honor of the god, calling it the Saturnalia, and that it was on the authority of this belief that Augustus, in his laws for the administration of justice, ordered the three days to be kept as rest days.
 Masurius and others believed that the Saturnalia were held on one day, the fourteenth day before the Kalends of January[=19th Dec.], and their opinion is corroborated by Fenestella when he says that the virgin Aemilia was condemned on the fifteenth day before the Kalends of January[=18th Dec.]; for, had that day been a day on which the festival of the Saturnalia was being celebrated, she could not by any means have been called on to plead,  and he adds that “the day was the day which preceded the Saturnalia,” and then goes on to say that “on the day after that, namely, the thirteenth day before the Kalends of January [=20th Dec.], the virgin Licinia was to plead,” thereby making it clear that the thirteenth day too was not a festival. …
[ 18] One can infer, then, from all that has been said, that the Saturnalia lasted but one day and was held only on the fourteenth day before the Kalends of January [=19th Dec.]; it was on this day alone that the shout of “Io Saturnalia” would be raised, in the temple of Saturn, at a riotous feast. …
 I think that we have now given abundant proof that the festival of the Saturnalia used to be celebrated on only one day, the fourteenth before the Kalends of January [=19th Dec.], but that it was afterward prolonged to last three days: first, in consequence of the days which Caesar added to the month of December, and then in pursuance of an edict of Augustus which prescribed a series of three rest days for the Saturnalia. The festival therefore begins on the sixteenth day before the Kalends of January [=17th Dec.] and ends on the fourteenth [=19th Dec.], which used to be the only day of its celebration.  However, the addition of the feast of the Sigillaria has extended the time of general excitement and religious rejoicing to seven days. …
Chap. 11. … I must now deal briefly with the Sigillaria, for I would not have you think that I spoke of a matter calling for a smile rather than reverence.
 Epicadus relates that Hercules after killing Geryon drove his herds in triumph through Italy and from a bridge (now known as the Sublician Bridge), which had been built for the occasion, cast into the river a number of human figures equal to the number of the comrades he had chanced to lose on his journey, his object being to ensure that these figures might be carried by the current to the sea and so, as it were, to restore to their ancestral homes the bodies of the dead. This is said to have been the origin of the practice, which has persisted, of including the making of such figures in a religious rite.
 In my opinion, however, a truer account of the origin of this practice is that which, I remember, I recently recalled, namely, that, when the Pelasgians learned, by a happier interpretation of the words, that “heads” meant heads of clay not heads of living men and came to understand that photos meant “of a light” as well as “of a man,” they began to kindle wax tapers in honor of Saturn, in preference to their former ritual, and to carry little masks to the chapel of Dis, which adjoins the altar of Saturn, instead of human heads.
 Thence arose the traditional custom of sending round wax tapers at the Saturnalia and of making and selling little figures of clay for men to offer to Saturn, on behalf of Dis, as an act of propitiation for themselves and their families.  So it is that the regular use of such articles of trade begins at the Saturnalia and lasts for seven days.
These days, in consequence, are only rest days (feriatos), not all of them are festivals. For we have shown that the day in the middle, namely the thirteenth day before the Kalends of January [=20th Dec.], was a day for legal business; and this has been attested by other statements made by those who have given a fuller account of the arrangement of the year, months, and days, and of the regulation of the calendar by Gaius Caesar.
-  Macrobius: The Saturnalia, translated by Percival Vaughan Davies, Columbia University Press, 1969 ↩