The absorption of neighboring local gods took place as the Roman state conquered the surrounding territory. The Romans commonly granted the local gods of the conquered territory the same honors as the earlier gods of the Roman state religion. In addition to Castor and Pollux, the conquered settlements in Italy seem to have contributed to the Roman pantheon Diana, Minerva, Hercules, Venus, and deities of lesser rank, some of whom were Italic divinities, others originally derived from the Greek culture of Magna Graecia. In 203 BC, the cult object embodying Cybele was brought from Pessinus in Phrygia and welcomed with due ceremony to Rome, centuries before the territory was annexed formally. Both Lucretius and Catullus, poets contemporary in the mid-1st century BC, offer disapproving glimpses of her wildly ecstatic cult.
In some instances, deities of an enemy power were formally invited through the ritual of evocatio to take up their abode in new sanctuaries at Rome.
Communities of foreigners (peregrini) and former slaves (libertini) continued their own religious practices within the city. In this way Mithras came to Rome and his popularity within the Roman army spread his cult as far afield as Roman Britain. The important Roman deities were eventually identified with the more anthropomorphic Greek gods and goddesses, and assumed many of their attributes and myths.