An augur was originally a priest who used birds for divination. The art of the augur was called ius augurium (augury) or auspicium. The famous Greek biographer Plutarch (c. A.D. 45-120) says the augur was originally called an auspex.
The job of the augur was to interpret divine will by means of signs in nature and to predict the future by means of interpreting animal entrails.
Romulus, king and also an augur, (or Numa Pompilius, the second king of Rome) established an initial college (collegium) of three augurs. The collegium in number to 9 by 300 B.C. and to 15 under Sulla, c. 81 B.C. The augurs handed down the rules of their art to new members whom they elected for life. In 103 B.C. they had their right to self-elect taken away.
The augur was important because he determined whether the gods approved military and political acts. He also marked sacred areas (templa).
References:
Lesley and Roy Adkins: "Dictionary of Roman Religion"
