I was inspired to look at an English translation of Macrobiuss Saturnalia after reading Roger Pearses post that mentioned that Macrobius claimed that an infant was presented on the winter solstice as a representation of the Sun. Saturnalia was a Roman feast which occurred in middle or late December, and many have tried to draw ties between this feast and the institution of the date of Christmas.
The Saturnalia by Macrobius (wrote early 5th century) is really a dinner conversation by several interlocutors that is set during the festival Saturnalia. The lengthy dialogue covers all manner of Roman culture and the festival of Saturnalia is only one of the many, many topics. The translation I used is the one by Percival Vaughn Davies published in 1969 by Columbia University press. Loeb just came out with the only other translation; it uses a superior text and I assume has better editors. The Davies translation does not even include quotation marks!
In this work there are some very good, but lengthy quotes about the origins of Saturnalia and its customs and dates, so I will publish it all in two or three blog posts.
We begin in Saturnalia 1.7.18 which discusses the origins of the festival:
The laws of religion, he said, allow me to disclose the origin of the festival of the Saturnalia so far as the account of its origin is a matter of mythology or is made known to all by the physicists
In the omitted section Macrobius discusses, through an interlocutor, how Saturn and Janus coreigned in Italy.
 It was during their reign that Saturn suddenly disappeared, and Janus then devised means to add to his honors. First he gave the name Saturnia to all the land which acknowledged his rule; and then he built an altar, instituting rites as to a god and calling these rites the Saturnalia—a fact which goes to show how very much older the festival is than the city of Rome. And it was because Saturn had improved the conditions of life that, by order of Janus, religious honors were paid to him, as his effigy indicates, which received the additional attribute of a sickle, the symbol of harvest.
 Saturn is credited with the invention of the art of grafting, with the cultivation of fruit trees, and with instructing men in everything that belongs to the fertilizing of the fields. Furthermore, at Cyrene his worshipers, when they offer sacrifice to him, crown themselves with fresh figs and present each other with cakes, for they hold that he discovered honey and fruits. Moreover, at Rome men call him Sterculius, as having been the first to fertilize the fields with dung (stercus).  His reign is said to have been a time of great happiness, both on account of the universal plenty that then prevailed and because as yet there was no division into bond and free—as one may gather from the complete license enjoyed by slaves at the Saturnalia.
Then Macrobius adds a second tradition about the origins of the festival:
 Another tradition accounts for the Saturnalia as follows. Hercules is said to have left men behind him in Italy, either (as certain authorities hold) because he was angry with them for neglecting to watch over his herds or (as some suppose), deliberately, to protect his altar and temple from attacks. Harassed by brigands, these men occupied a high hill and called themselves Saturnians, from the name which the hill too used previously to bear, and, conscious of the protection afforded to them by the name of Saturn and by the awe which the god inspired, they are said to have instituted the Saturnalia, to the end that the very observance of the festival thus proclaimed might bring the uncouth minds of their neighbors to show a greater respect for the worship of the god.
Macrobius then adds a third account:
 I am aware too of the account given by Varro of the origin of the Saturnalia. The Pelasgians, he says, when they were driven from their homes, made for various lands, but most of them flocked to Dodona and, doubtful where to settle, consulted the oracle. They received this reply: Go ye in search of the land of the Sicels and the Aborigines, a land, sacred to Saturn, even Cotyle, where floateth an island. Mingle with these people and then send a tenth to Phoebus and offer heads to Hades and a man to the Father.8 Such was the response which they received, and after many wanderings they came to Latium, where in the lake of Cutilia they found a floating9 island,  for there was a large expanse of turf—perhaps solidified mud or perhaps an accumulation of marsh land with brushwood and trees forming a luxuriant wood—and it was drifting through the water by the movement of the waves in such a way as to win credence even for the tale of Delos, the island which, for all its lofty hills and wide plains, used to journey through the seas from place to place.  The discovery of this marvel showed the Pelasgians that here was the home foretold for them. And, after having driven out the Sicilian inhabitants, they took possession of the land, dedicating a tenth of the spoil to Apollo, in accordance with the response given by the oracle, and raising a little shrine to Dis and an altar to Saturn, whose festival they named the Saturnalia.
 For many years they thought to propitiate Dis with human heads and Saturn with the sacrifice of men, since the oracle had bidden them: Offer heads to Hades and a man (<pfi>xa) to the Father. But later, the story goes, Hercules, returning through Italy with the herds of Geryon, persuaded their descendants to replace these unholy sacrifices with others of good omen, by offering to Dis little masks cleverly fashioned to represent the human face, instead of human heads, and by honoring the altars of Saturn with lighted candles instead of with the blood of a man; for the word (porta means lights as well as a man.  This is the origin of the custom of sending round wax tapers during the Saturnalia, although others think that the practice is derived simply from the fact that it was in the reign of Saturn that we made our way, as though to the light, from a rude and gloomy existence to a knowledge of the liberal arts.  I should add, however, that I have found it written that, since many through greed made the Saturnalia an excuse to solicit and demand gifts from their clients, a practice which bore heavily on those of more slender means, one Publicius, a tribune, proposed to the people that no one should send anything but wax tapers to one richer than himself.
Here another interlocutor interrupts and talks about different traditions that were added at a later time:
 I find, Praetextatus, interposed Albinus Caecina, a substituted sacrifice, such as that which you have just mentioned, made in later times at the rites of the Compitalia, when games used to be held at crossroads throughout the city, that is to say, on the restoration of these games by Tarquinius Superbus, in honor of the Lares and of Mania, in accordance with an oracle of Apollo. For that oracle ordained that offering should be made for heads with heads,  and for some time the ritual required the sacrifice of boys to the goddess Mania, the mother of the Lares, to insure the safety of the family. But after the expulsion of Tarquinius, Junius Brutus, as consul, determined to change the nature of the sacrificial rite. By his order heads of garlic arid poppies were used at the rite, so that the oracle was obeyed, in so far as it had prescribed heads, and a criminal and unholy sacrifice was discarded.10 It also became the practice to avert any peril that threatened a particular family by hanging up woolen11 images before the door of the house. As for the games themselves, they were customarily called Compitalia from the crossroads (compita) at which they were held. But I interrupted you. Pray go on.
Then Macrobiuss main interlocutor for this section continues with his conclusion:
 You have referred, said Praetextatus, to a parallel instance of a change for the better in the ritual of a sacrifice. The point is well taken and well timed. But from the reasons adduced touching the origin of the Saturnalia it appears that the festival is of greater antiquity than the city of Rome, for in fact Lucius Accius in his Annals says that its regular observance began in Greece before the foundation of Rome.  Here are the lines:
In most of Greece, and above all at Athens, men celebrate in honor of Saturn a festival which they always call the festival of Cronos. The day is kept a holiday, and in country and in town all usually hold joyful feasts, at which each man waits on his own slaves. And so it is with us. Thus from Greece that custom has been handed down, and slaves dine with their masters at that time.
So, lots of traditions about the origin of the festival of Saturnalia, but none of them seem to have to do with the birth of anyone. Tomorrow I will post Macrobiuss discussion on the various dates Saturnalia was celebrated and we will see if according to Macrobius it was ever celebrated on December 25.