Traditionally they had been established by Romulus, the first King. They knew the appropriate procedure for 'taking the auspices', by observing the flight of birds - and for their interpretation when taken. Their number historically varied from 3 to 15 and they held their office for life. They were religious officials expert on auguria - signs encouraging or discouraging a particular course of action. An approved action was 'fas' or promising, favorable, and religiously permitted. By contrast, an unfavorable action was 'nefas', not permitted. No business, public or private, could be transacted on a day that was 'nefas'. Augury was a science; a science the understanding of which was contained in special books.

In his observation of birds the augur actually did not confine himself to noticing their flight. The birds were distinguished in two main categories, the alites and oscines. The alites were birds like eagles and vultures, which gave signs by their manner of flying. The oscines were birds that gave signs by their cry; like ravens, sparrows, owls and crows. There were also birds sacred to some particular God, and the mere appearance of which was an omen of good and evil.