This legendary incident took place, presumably, during the Samnite wars, circa 340 B.C.
The Roman consuls, before they led their troops into the battle, offered sacrifices. It is said that the
soothsayer [haruspex] pointed out to Decius that the head of the liver was on the friendly [right]
side, that the victim was in other respects acceptable to the gods, and that the sacrifice of Manlius
had been most favourable. 'It will do,' said Decius, 'if my colleague has received favourable omens.'
In the formation above described they advanced into the field. Manlius commanded the right wing,
Decius the left. At first the battle was fought with equal strength and ardour on both sides; but after
a time the Roman hastati [spearmen] on the left, unable to resist the pressure of the Latins, fell back
upon the principes [i.e., the heavy armed troops]. In this instant of alarm Decius the consul shouted
with a loud voice to Marcus Valerius: 'We need help from the gods, Marcus Valerius ! Come, state
[or public] pontiff of the Roman people, dictate the words, so that I can devote myself for [i.e., save]
the legions.' The pontiff bade him put on the purple-bordered toga and veil his head, with one hand
thrust out from beneath the toga and touching his chin, and standing upon a spear that was laid
beneath his feet to say as follows: 'Janus, Jupiter, Father Mars, Quirinus, Bellona, Lares, Divi
Novensiles, Di Indigites, gods in whose power are both we and our enemies, and you also, Di
Manes-I invoke and implore you, your favour I beg and beseech, that you may prosper the power
and the victory of the Roman people of the Quirites, and visit upon the foes of the Roman people
of the Quirites terror, fear, and death. As I have pronounced the words, even so on behalf of [pro,
in lieu of] the republic of the Roman people of the Quirites, the army, the legions, and the auxiliaries
of the Roman people of the Quirites, I hereby devote the legions and auxiliaries of the enemy,
together with myself, to the Di Manes and to Earth [Tellus].'
Having uttered this prayer, he ordered the lictors to go to Titus Manlius at once and announce to his colleague that he had devoted himself for the good of the army. Then, girding himself with the Gabinian cincture and leaping, armed, upon his horse, he plunged into the thick of the enemy, a conspicuous sight to both armies and with something about him more August than human, as though he had been sent from heaven to expiate all the anger of the gods, and to avert destruction from his people -and turn it upon their enemies. Thus the greatest terror and dread accompanied him, and, throwing the Latin front into disorder, it at once spread deeply into their whole army. This was most dearly evident from the fact that wherever he rode, men trembled as if struck by some baleful star; and when he fell beneath a hail of missiles, in that instant there could he no doubt of the consternation of the Latin cohorts, which everywhere deserted the field and took to flight. At the same time the Romans-their spirits now set free from religious fears-pressed on as if only then the signal had been given for the first time, and delivered a united blow. The light- armed men were running out between the first two ranks of foot soldiers and were adding their strength to that of the spearmen and the heavy armed troops, while the troops in the third rank, kneeling on their right, knees, were waiting for the consul to signal them to rise [and advance]. . . .
For the rest, among all the citizens and allies the chief praise in that war belongs to the consuls, of whom one [Decius] had drawn upon himself above all the threats and dangers belonging to the gods above and the gods below, while the other had shown such courage and skill in battle that of those Romans and Latins who have handed down a report of the conflict all agree that whichever side was led by Titus Manlius would surely have won. The Latins fled to Minturnae. After the battle their camp was captured and many men-mostly Campanians-were seized and put to death there. The body of Decius could not be found that day, and night fell while the search continued. On the following day it was discovered in a great heap of enemy dead, covered with missiles, and was given burial by his colleagues in a manner befitting his death.
It seems appropriate at this point to add that the consul, dictator, or praetor who devotes the
legions of the enemy need not also devote himself, but may instead devote any citizen he chooses
from an enlisted Roman legion. If this man is killed, it is proof that all is well. If he does not die,
then an image (signum) of him is buried seven feet or more beneath the ground and a sacrifice
(piaculum, sin offering] is slain; and where the image is buried no Roman magistrate may lawfully
ascend [i.e., upon the tumulus].
But if he chooses to devote himself, as Decius did, but does not die, he cannot rightly offer sacrifice either for himself or for the people, whether it is with a sacrificial victim or something else that he wishes to offer. The one who devotes himself may dedicate his arms to Vulcan or to any other god he chooses [as a rule, the enemies' weapons were dedicated to Vulcan]. The spear on which the consul had stood and prayed must not be allowed to fall into enemy hands. If this happens, expiation must be made to Mars, with swine, sheep and bull [Marti suovetaurilibus piaculum fieri]. These details, though the memory of both divine and human customs has now been wiped out by the preference shown to new and foreign ways rather than to the ancient and ancestral, I have thought it worth while to relate in the very words which were fashioned and handed down [from the days of old].
Translation by Frederick C. Grant, in his Ancient Roman Religion, Library of Religion
paperbook series (New York, 1957), PP. 23-5