On August 3, at the Romans’ Supplicia canum, sacrificial dogs tied to elder-wood forks were paraded between the temples of Iuventus and Summanus. The rationale was to punish descendants for the sins of their ancestors — the dogs who had failed to perform their primary duty, as watchdogs. On one momentous occasion, when the Gauls under Brennus had assailed the Capitol, it is said that the dogs failed to bark.
47. While1 these proceedings were taking place at Veii, the Citadel and Capitol of Rome were in imminent  danger. The Gauls had either noticed the footprints left by the messenger from Veii, or had themselves discovered a comparatively easy ascent up the cliff to the temple of Carmentis. Choosing a night when there was a faint glimmer of light, they sent an unarmed man in advance to try the road; then handing one another their arms where the path was difficult, and supporting each other or dragging each other up as the ground required, they finally reached the  summit. So silent had their movements been that not only were they unnoticed by the sentinels, but they did not even wake the dogs, an animal peculiarly sensitive to nocturnal  sounds. But they did not escape the notice of the geese, which were sacred to Juno and had been left untouched in spite of the extremely scanty supply of food. This proved the safety of the garrison, for their clamour and the noise of their wings aroused M. Manlius, the distinguished soldier, who had been consul three years before. He snatched up his weapons and ran to call the rest to arms, and while the rest hung back he struck with the boss of his shield a Gaul who had got a foothold on the summit and knocked him  down. He fell on those behind and upset them, and Manlius slew others who had laid aside their weapons and were clinging to the rocks with their hands. By this time others had joined him, and they began to dislodge the enemy with volleys of stones and javelins till the whole body fell helplessly down to the  bottom. When the uproar had died away, the remainder of the night was given to sleep, as far as was possible under such disturbing circumstances, whilst their peril, though past, still made them  anxious.
Although the dogs might have been asleep, the Romans may have received their warning: through the honking of geese. It is also possible, the Romans took a bloodbath, but the popular version (and it does make a nice story) honors the geese, and so purple and gold clothed geese were carried around, during the sacrifice of the dogs.
We have already1 spoken of the honours earned by the geese, when the Gauls were detected in their attempt to scale the Capitol. It is for a corresponding reason, also, that punishment is yearly inflicted upon the dogs, by crucifying them alive upon a gibbet of elder, between the Temple of Juventas2 and that of Summanus.3
Pliny the Elder, The Natural History
John Bostock, M.D., F.R.S., H.T. Riley, Esq., B.A., Ed. Book XXIX.14
Dogs were used as scapegoats and folk cures, sometimes as we might use lab rats, so although this patriotic legend may be fanciful, punishment of dogs for failing to alert the Romans to the imminent loss of the Capitol is not outside the realm of possibility.
Contrast this August 3 festival with a more dog-loving annual event in Nepal:
“In Nepal, Diwali is called Tihar. Similar to other Diwali observances, lamps are lit at night during Tihar. The festival of lights celebrates the triumph of light over darkness, of knowledge over ignorance, and the dissolution of barriers that separate humans from authentic experience of the world. Nepalese Hinduism is unique in dedicating the second day of Tihar, Kukur Tihar, to the worship of dogs.”
Nepal’s Kukur Tihar Festival Is Diwali for Dogs
In 2015, Tihar/Diwali starts on November 11 for Nepal and most of India.
“It has been suggested that the story of Manlius* and the geese is aetiological, either to explain the ritual of the geese and the dogs, or to account for the cognomen Capitolinus among the Manlii. The cognomen predates the hero of 390 and is most simply explained from the fact that the Manlii lived there.”
* Marcus Manlius Capitolinus, defender of the Roman arx [citadel on the northern spur of the Capitoline Hill], consul, and social reformer was thrown to his death from the Tarpeian rock in 384 BC. The Tarpeian Rock is believed to have been somewhere on the Capitoline. The Tarpeian Rock form of execution was reserved for murderers and traitors.
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