While the Ludi Apollinares continued, this day in ancient Rome also celebrated the Nonae Caprotinae -- Nonae because July is one of the months when the nones fell on the 7th instead of the 5th and Caprotinae because of some ancient connection to goats. Probably.
The animals in question might have been boars or swine, which might possibly make more sense given the location -- a swamp. The Nonae Caprotinae was a festival to Juno (possibly dressed in animal skins) celebrated in the Campus Martius (field of Mars) under a wild fig tree, branches of which women tore down, a process called a vitulatio (Varro L.L6.18). The marshy site is known as the Palus (swamp) Caprae, which is where Romulus was supposed to have vanished, as mentioned in connection with the Poplifugia earlier this month. There is a legendary connection between the heroism of women, especially slave women in the aftermath of the Gallic invasion, and the holiday.
" Of this war two different accounts are given; I shall begin with the more fabulous. They say that the Latins (whether out of pretense, or a real design to revive the ancient relationship of the two nations) sent to desire of the Romans some free-born maidens in marriage; that when the Romans were at a loss how to determine (for on one hand they dreaded a war, having scarcely yet settled and recovered themselves, and on the other side suspected that this asking of wives was, in plain terms, nothing else but a demand for hostages, though covered over with the specious name of intermarriage and alliance), a certain handmaid, by name Tutula, or, as some call her, Philotis, persuaded the magistrates to send with her some of the most youthful and best looking maid-servants, in the bridal dress of noble virgins, and leave the rest to her care and management; that the magistrates consenting, chose out as many as she thought necessary for her purpose, and, adorning them with gold and rich clothes, delivered them to the Latins, who were encamped not far from the city; that at night the rest stole away the enemy's swords, but Tutula or Philotis, getting to the top of a wild fig-tree, and spreading out a thick woolen cloth behind her, held out a torch towards Rome, which was the signal concerted between her and the commanders, without the knowledge, however, of any other of the citizens, which was the reason that their issuing out from the city was tumultuous, the officers pushing their men on, and they calling upon one another's names, and scarce able to bring themselves into order; that setting upon the enemy's works, who either were asleep or expected no such matter, they took the camp, and destroyed most of them; and that this was done on the nones of July, which was then called Quintilis, and that the feast that is observed on that day is a commemoration of what was then done. For in it, first, they run out of the city in great crowds, and call out aloud several familiar and common names, Caius, Marcus, Lucius, and the like, in representation of the way in which they called to one another when they went out in such haste. In the next place, the maid-servants, gaily dressed, run about, playing and jesting upon all they meet, and amongst themselves, also, use a kind of skirmishing, to show they helped in the conflict against the Latins; and while eating and drinking, they sit shaded over with boughs of wild fig-tree, and the day they call Nonae Caprotinae, as some think from that wild fig-tree on which the maid- servant held up her torch, the Roman name for a wild fig-tree being caprificus. Others refer most of what is said or done at this feast to the fate of Romulus, for, on this day, he vanished outside the gates in a sudden darkness and storm (some think it an eclipse of the sun), and from this, the day was called Nonae Caprotinae, the Latin for a goat being capra, and the place where he disappeared having the name of Goat's Marsh, as is stated in his life."
"The Prehistoric Roman Calendar," by Van L. Johnson. The American Journal of Philology, Vol. 84, No. 1 (Jan., 1963), pp. 28-35.
"Vitvlatio," by J. Whatwough. Classical Philology, Vol. 18, No. 4 (Oct., 1923), pp. 350-351.
"A New Epithet of Juno," by J. Whatmough. The Classical Quarterly, Vol. 16, No. 3/4 (Jul. - Oct., 1922), p. 190.