Early Astrology

A lot of the way in which Astrology is practices is a legacy from the cult of Pythagorus.
They believed that universal truths could be extracted from finding constants in numbers and nature and therefore ascribed magic to certain numbers and number patterns.

Odd numbers were favoured (they can add up to form even numbers or more odd numbers if more than two numbers are added but even numbers can never add up to be odd)
e.g.

1+1 = 2
1+1+1 = 3

2+2 = 4
2+2+2 = 6

Odd signs i.e Fire and Air were deemed positive (masculine and agressive) whereas even signs were deemed as negative (feminine and passive).

The houses are divisions of the visible heavens as seen at any point of time at any place of the Earth, with a corresponding division of the invisible heavens beneath the Earth.
The Equal House system, where all 12 houses are equally divided into 30 degrees each with the degree of the Ascendant as the starting degree of each of the houses in their respective signs. This system was attributed to Ptolemy (70-140 CE).

The most commonly used system in the West is that of Porphyry in which the houses are determined by the horizon and meridian where sections of the ecliptic in between are trisected.

In the ancient world horoscopes (birth-charts) were drawn up not for consultation as they are now but for predictions or help with specific decisions. Astrology was an aristocratic form of divination.
There tended to be some concentration on the bizarre and dramatic (i.e violent deaths and sexual perversions).
During the time of the Roman Empire there were specialists in predicting the winners of the chariot races. Prediction of the time and mode of death was also popular, despite being illegal. It was also useful in correspondence with spell and charm making, for example a contraceptive spell was said to be best performed during a waning moon in a female sign on a day of Saturn or Mercury for optimum results.
Astrology went through periods of popularity and infamy in Rome however.
There were times when all the astrologers, philosophers and metics (foreigners) were expelled from the city of Rome in times of over-population and food shortages.
The Stoic school of philosophy gained a lot of respect for the practise of astrology whereas the Epicureans were hostile to it, as with all forms of divination. The Jewish had divided opinions towards it and there are references to Astrology in the Dead Sea Scrolls.

Publius Nigidius Figulus revived Pythagoreanism, Tiberius was an ardent believer despite the fact that he was very non-religious but alas for Caesar whose scepicism caused him to ignore the warning of the Ides of March.

The early church saw divination and astrology in particular as a threat to their authority as a means of discovering the future.
They decided that determinism of human behaviour was through God NOT any other influences such as the planets. Propagandists wrote that astrology had been introduced by fallen angels in order to decrease it's popularity.

Of course as with any form of speculation on the future some people will believe things to such a degree that they will visit upon themselves self-fulfilling prophecies throgh fatalism.
There is an account of one astrologer who had calculated the time of his own death. Finding himself still attached to his mortal coil at the predicted hour he hanged himself.
There was another tale of an astrologer in ancient Rome that was asked to predict his own death by the emperor. The astrologer predicted that his body would be eaten by wild beasts whereupon the emperor ordered his murder in order to disprove the man. However birds and other wild animals came to scavenge the body proving the unfortunate man correct.

Prophecies didn't always come through with their divine sanctions.
Such was the case of the consul Octavius, a supporter of Sulla. When he was killed a chart was found in his possession which he had believed assured him his safety.

BIBLIOGRAPHY

Barton, Tasmin - Ancient Astrology (1994)
Carter, Charles E. O. - The Principles of Astrology (1971)
Dill, Samuel - Roman society from Nero to Marcus Aurelius (1911)