The true religion of Rome, the Roman State religion, was totally opposed to "sorcery" and "magic" of any sort. The Roman state religion also condemned astrology and "foreign superstitions" of all kinds. This is not to say that there were no "sorcerers" or "magicians" -- or astrologers -- in Rome. But it was not lawful for them to practice their arts under most of Roman history.

Now… we are looking at a period in excess of 1,000 years when we speak of ancient Rome, and what was true in 300 B.C. was not necessarily the law in 300 A.D. Also, just because a law was on the books doesn't mean it was enforced. Tiberius, for example, had a personal astrologer. So did several other emperors. However, Cato the Censor would have been horrified at the idea that an astrologer should have any part in advising a Roman ruler…but he was long dead before Tiberius was born.

Religio literally meant "re-bind" to the Romans. It was the connection between the gods who kept Rome strong and the Roman state. The various colleges of priests were charged with maintaining order, not with working magic. That would have been forbidden practice and highly offensive to the gods. It would have been superstitio--which was a very bad thing. You could be executed for superstitio.

Taking the omens and the auspices was a different matter. That was communication with the gods to learn their will. The impiety of certain military commanders was not in manipulating the auspices or the omens--it was their sacrilege in manipulating them without proper regard to the rules.

For example, you could perform a sacrifice fifty times if necessary -- until it came out "right" and the liver and entrails of the animal said what you needed them to say. What you could NOT do was violate the terms of the communication medium. There was once a military commander who became incensed when the sacred chickens refused to eat--a very bad omen indeed for the outcome of a battle. So, saying, "If they won't eat let them drink!" he tossed the chickens into the sea and they drowned. He went on to fight the battle and lost disastrously. But, according to the traditional teachings, it was his own fault for ignoring the omens and committing the sacrilege of murdering the sacred chickens. What he should have done is found a better class of chickens who were hungry and would therefore have provided the proper result.

In any event…none of this was "magic" -- it was merely "communication with the gods."