The Roman mythology is the combination of the beliefs, the rituals, and the observances of supernatural occurences by the ancient Romans from early periods until Christianity finally completely replaced the native religions of the Roman Empire.
The religion of the early Romans was so changed by the addition of numerous and conflicting beliefs in later times and by the assimilation of a vast amount of Greek mythology that it cannot be ever reconstructed precisely. This was because of the extensive changes in the religion before the literary tradition began.
The origins of those myths were in most cases unknown to the early Roman writers on religion. On the other hand classical writers, such as the poet Ovid in his Fasti (Calendar), were strongly influenced by Hellenistic models and in their works they frequently employed Greek beliefs to fill gaps in the Roman tradition.