In the religions of ancient Rome, an omen, plural omina, was a sign intimating the future, considered less important to the community than a prodigium but of great importance to the person who heard or saw it.
Omina could be good or bad. Unlike prodigies, bad omina were never expiated by public rites but could be reinterpreted, redirected or otherwise averted. Some time around 282 BC, a diplomatic insult formally "accepted as omen" was turned against Tarentum and helped justify its conquest. A thunderclap cost Marcellus his very brief consulship (215 BC): thereafter he traveled in an enclosed litter when on important business, to avoided sight of possible bad omens that might affect his plans. Bad omens could be more actively dealt with, by countersigns or spoken formulae. Before his campaign against Perseus of Macedon, the consul L Aemilius Paullus was said to have heard of the death of Perseus, his daughter's puppy. He interpreted this as a favourable omen and defeated King Perseus at the Battle of Pydna (168 BC).
Some evidently took omens very seriously. Others did not, or failed to avert bad omens and were thought to have paid the ultimate price. In 217 BC the consul Flaminius "disregarded his horse's collapse, the chickens, and yet other omens, before his disaster at Lake Trasimene". Licinius Crassus took ship for Syria despite the ominous call of a fig-seller – "Cauneas!" ("Caunean figs!"), which might be heard as "Cave ne eas!" ("Beware, don't go!") – and was killed on campaign. Cicero saw these events as merely coincidental; only the credulous could think them ominous. though by his time, politicians, military magnates and their supporters actively circulated tales of excellent omens that attended their births and careers.