Religion in ancient Rome combined several different cult practices and embraced more than a single set of beliefs.
The Romans originally followed a rural animistic tradition, in which many spirits (gods) were each responsible for specific, limited aspects of the cosmos and human activities. For example, there were different gods for ploughing, for horses, and for cattle. See Faun. The Etruscans provided the context out of which Roman culture and religious beliefs evolved. See Etruscan mythology.
Another aspect of this animistic belief was ancestor worship, with each family honouring their own dead by their own rites. See Genius
Early in the history of the Roman Republic, foreign gods were imported, especially from Greece, which had a great cultural influence on the Romans after they conquered it. In addition, the Romans connected some of their indigenous deities with Greek gods and goddesses. Some important ones, with the Greek equivalents in parentheses, were Jupiter (= Zeus), Juno (= Hera), Minerva (= Athena), Mars (= Ares), Vesta (= Hestia), Saturn (= Kronos), Vulcan (= Hephaistos), Cupid (= Eros), and Neptune (= Poseidon)and Dionysus or Bacchus in Rome
As the Roman Empire expanded, and included people from a variety of cultures, there were more and more gods. The legions brought home cults originating from Egypt, Britain, Iberia, Germany, and Persia. The cults of Cybele Isis and Mithras were particularly important.
Along with this, the ancient Roman beliefs and practices continued, especially in and around Rome itself. This included the worship of the lares and penates (spirits specific to a family, with altars in the home), festivals such as the Lupercalia and Saturnalia, and a complex system of lucky and unlucky days.
Another important aspect of religion in Roman times was the divinity of the Emperor. More than just being the Pontifex Maximus (the head of the Roman Religion), Roman Emperors endorsed the various popular cult religions. In an effort to enhance political loyalty among the populace, they often called subjects to participate in the cults and revere the emperors as gods. Examples of this include "The Achievements of the Divine Augustus", which are two large bronze pillars in Rome inscribed with the deeds of Augustus, roman coins where the Emperor is portrayed with a halo or divine glow, temple inscriptions such as "Divine Augustus Caesar, son of a god, imperator of land and sea..." (Roman Temple Inscription in Myra, Lycia).
Eventually, Christianity came to replace the older pantheon as the state religion.