The Romans and the various peoples they were in contact with each "...possessed a national μαντική or divinatio, which was supported by the laws and institutions of the state, and which was guarded from mixture with foreign elements by stringent enactments."
The distinctive and primary form of Roman divination was the auspicium, but other types of divination were also used. Oracles of the Greek type were not much used by Romans, but possibly because of influence from the Etruscans, Romans were attentive to signs in nature.
Public divination in the period of the late Republic consisted of a specific set of procedures that were performed by specific individuals under specific circumstances, but always in connection with some public act or situation that affected the whole of the state.
Public divination was not designed to reveal the future, but only to ascertain the will of the gods for determining what action to take in a given situation.
Auspicia (from aves, birds and specto, to see) consisted of observation of birds and certain other natural phenomena.
Before performing any public act (e.g., calling a comitia, starting a battle) a magistrate consulted the gods by "taking the auspices". The magistrates themselves performed these "auspicia impetrativa", and it was up to them to determine how to interpret what they saw. Augurs served two roles; they could be consulted by magistrates regarding any questions related to the auspices, and the augurs were responsible for creating and inaugurating the auguracula, the spaces in and from which the auspices were taken.
Auspicia impetrativa were narrow in scope, only indicating simple approval or disapproval by the gods of a specific course of action that a magistrate proposed to undertake. These auspices were also limited in space and time since they were valid for one day only and only until the magistrate crossed certain boundaries, such as that between the Campus Martius and the city proper, the amnis Petronia . Once such a boundary was crossed, the auspices had to be taken again.
Whereas auspicia impetrativa were initiated by magistrates, auspicia oblativa were manifested by the gods themselves. Any seemingly significant or unusual human or natural event could be seen as an auspicium oblativum. The most extreme of these could be considered as prodigies. Auspicia oblativa might be observed by a magistrate directly, or they might be brought to the notice of a magistrate. Except for often in the case of prodigies, the magistrate could decide to accept or reject the auspicium oblativum.
In the case of prodigies, the Senate could instruct the caretakers of the Sibylline Books to consult them and then report what they found to the Senate. The Senate would then vote on what action to take. Smith's Dictionary cites Niebuhr as contrasting these oracles, the purpose of which was "to learn what worship was required by the gods" with those of the Greeks which were used to predict future events.
Under normal circumstances, foreign cults were restricted to the area outside the pomerium, but the strength of the Sibylline books was such that their recommendations permitted the introduction of foreign cults (e.g., Magna Mater) within the pomerium.
Extispicy and Haruspicy
"Extispicy" denotes the inspection by the person officiating at a sacrifice of the exta (entrails) of a sacrificial victim. If anomalies were present, the sacrifice was deemed to be not acceptable to the gods. Another victim would be chosen and the sacrifice was repeated. A more detailed examination of the entrails is "haruspicy" the origin of which may be found in the Etruscan practice of haruspicy.
Under exceptional circumstances the Senate could vote to send a delegation to an oracle. Upon return of the delegation, the Senate would hear its report and then vote on what action to take.
Divination of many sorts permeated the private life of Romans.
Regarding private auspices, Cicero wrote, "In ancient times scarcely any matter out of the ordinary was undertaken, even in private life, without first consulting the auspices...".
Aulus Gellius cites Lucius Cincius on enlistment procedures, including among the exemptions "auspices it is not permitted to pass without a piaculum."
Consistent with the time limitation of auspices, the recruit was required to appear on the next day.
Beard, M., 1986. Cicero and divination: the formation of a Latin discourse JRS 76, 33-46
Brause, Francis Albert, 1875. Librorum de Disciplina Augurali ante Augusti Mortem Scriptorum Reliquiae. A Thesis on the extant literary fragments that describe and/or detail augural practice from before the death of Augustus.
Denyer, N., 1985. The case against divination: an examination of Cicero's de Divinatione. PCPhS 211, n.s. 31, 1-10
Krostenko, B., 2000. Beyond (Dis)belief: Rhetorical Form and Religious Symbol in Cicero's de Divinatione. TAPA 130, 353-391.
Lateiner, D. 2004. Signifying Names and Other Ominous Accidental Utterances in Classical Historiography. Greek Roman and Byzantine Studies vol. 45. Retrieved from http://www.duke.edu/web/classics/grbs/FTexts/45/Lateiner.pdf
Linderski, J., 1982. Cicero and Roman divination. La Parola del Passato 37, 12-38
Linderski, J., 1985. The augural law ANRW 16.3
Pease, A.S., 1920. Cicero. De Divinatione Libri Duo. Illinois Studies in Language and Literature 6, Urbana, Illinois.
Schofield, M., 1986. Cicero for and against divination JRS 76, 47-65
Wardle, D. (ed. & tr.), 2006. On Divination Book 1. Clarendon Ancient History Series. Oxford: Oxford University Press. Pp. xii + 469. ISBN 0199297916 Review by J. Linderski: http://www.classics.ukzn.ac.za/reviews/07-41war.htm Website: http://www.oup.com/us/catalog/general/series/ClarendonAncientHistorySeries/
- ↑ Smith's Dictionary: "Augur, Augurium"
- ↑ Overall discussion here is based primarily on Scheid, Chapter 7, except where noted.
- ↑ On the amnis Petronia and the auspices, see Festus 250: Petronia amnis est in Tiberim perfluens, quam magistratus auspicato transeunt, cum in Campo quid agere volunt, quod genus auspici peremne vocatur.
- ↑ William Smith, A Dictionary of Greek and Roman Antiquities (1875). Sibyllini Libri
- ↑ A delegation to the oracle at Delphi c. 398 BCE: Livy, V. 16
- ↑ Scheid, pg. 124: "Just as the magistrates and the Senate did, individuals resorted constantly to diviners."
- ↑ Cicero, De Divinatione 16  "Nihil fere quondam maioris rei nisi auspicato ne privatim quidem gerebatur, quod etiam nunc nuptiarum auspices declarant, qui re omissa nomen tantum tenent."
- ↑ "...auspiciumve quod sine piaculo praeterire non liceat..." Aulus Gellius, Noctes Atticae XVI. 4 http://www.csun.edu/~hcfll004/cincius.html