The augur was a priest and official in the classical Roman world. His main role was the practice of augury, interpreting the will of the gods by studying the flight of birds: whether they are flying in groups or alone, what noises they make as they fly, direction of flight and what kind of birds they are. This was known as "taking the auspices." The ceremony and function of the augur was central to any major undertaking in Roman society—public or private—including matters of war, commerce, and religion.
The Roman historian Livy stresses the importance of the augurs: "Who does not know that this city was founded only after taking the auspices, that everything in war and in peace, at home and abroad, was done only after taking the auspices?"
Although ancient authors believed that the term "augur" contained the words avis and gero—Latin for "directing the birds"—historical-linguistic evidence points instead to the root aug-: "to increase, to prosper."
Roman augurs were part of a college (Latin collegium) of priests who shared the duties and responsibilities of the position. At the foundation of the Republic in 510 BC, the patricians held sole claim to this office; by 300 BC, the office was open to plebeian occupation as well. Senior members of the collegium put forth nominations for any vacancies, and members voted on whom to co-opt.
In the Regal period tradition holds that there were three augurs at a time; by the time of Sulla, they had reached fifteen in number.
Augury sought the divine will regarding any proposed course of action which might affect Rome's pax, fortuna and salus (peace, good fortune and wellbeing). Political, military and civil actions were sanctioned by augury, historically performed by priests of the college of augurs and by haruspices on behalf of senior magistrates. The presiding magistrate at an augural rite thus held the “right of augury” (ius augurii). Magistracies (which included senior military and civil ranks) were therefore religious offices in their own right, and magistrates were directly responsible for the pax, fortuna and salus of Rome and everything that was Roman.