Interpretatio graeca (Latin, "Greek translation"), or "interpretation by means of Greek [models]", refers to the tendency of the ancient Greeks to identify foreign deities with their own gods.^[1][2] It is a discourse^[3] used to interpret or attempt to understand the mythology and religion of other cultures; a comparative methodology using ancient Greek religious concepts and practices, deities, and myths, equivalencies, and shared characteristics.

The phrase may describe Greek efforts to explain others' beliefs and myths, as when Herodotus describes Egyptian religion in terms of perceived Greek analogues, or when Dionysius of Halicarnassus and Plutarch document Roman cults, temples, and practices under the names of equivalent Greek deities. Interpretatio graeca may also describe non-Greeks' interpretation of their own belief systems by comparison or assimilation with Greek models, as when Romans adapt Greek myths and iconography under the names of their own gods.

Interpretatio romana is comparative discourse in reference to ancient Roman religion and myth, as in the formation of a distinctive Gallo-Roman religion. Both the Romans and the Gauls reinterpreted Gallic religious traditions in relation to Roman models, particularly Imperial cult.

Jan Assmann considers the polytheistic approach to internationalizing gods as a form of "intercultural translation":

The great achievement of polytheism is the articulation of a common semantic universe. ... The meaning of a deity is his or her specific character as it unfolded in myths, hymns, rites, and so on. This character makes a deity comparable to other deities with similar traits. The similarity of gods makes their names mutually translatable. ... The practice of translating the names of the gods created a concept of similarity and produced the idea or conviction that the gods are international.^[4]

Pliny the Elder expressed the "translatability" of deities as "different names to different peoples" (nomina alia aliis gentibus).^[5] This capacity made possible the religious syncretism of the Hellenistic era and the pre-Christian Roman Empire.

Herodotus was one of the earliest authors to engage in this form of interpretation. In his observations regarding the Egyptians, he establishes Greco-Egyptian equivalents that endured into the Hellenistic era, including Amon/Zeus, Osiris/Dionysus, and Ptah/Hephaestus. In his observations regarding the Scythians, he equates their queen of the gods, Tabiti, to Hestia, Papaios and Api to Zeus and Gaia respectively, and Argimpasa to Aphrodite Urania, while also claiming that the Scythians worshipped equivalents to Herakles and Ares, but which he does not name.

Some pairs of Greek and Roman gods, such as Zeus and Jupiter, are thought to derive from a common Indo-European archetype (Dyeus as the supreme sky god), and thus exhibit shared functions by nature. Others required more expansive theological and poetic efforts: though both Ares and Mars are war gods, Ares was a relatively minor figure in Greek religious practice and deprecated by the poets, while Mars was a father of the Roman people and a central figure of archaic Roman religion.

Some deities dating to Rome's oldest religious stratum, such as Janus and Terminus, had no Greek equivalent. Other Greek divine figures, most notably Apollo, were adopted directly into Roman culture, but underwent a distinctly Roman development, as when Augustus made Apollo one of his patron deities. In the early period, Etruscan culture played an intermediary role in transmitting Greek myth and religion to the Romans, as evidenced in the linguistic transformation of Greek Heracles to Etruscan Her[e]cle to Roman Hercules.

The phrase interpretatio romana was first used by the Imperial-era historian Tacitus in the Germania.^[6] Tacitus reports that in a sacred grove of the Nahanarvali, "a priest adorned as a woman presides, but they commemorate gods who in Roman terms (interpretatione romana) are Castor and Pollux."^[7] Elsewhere,^[8] he identifies the principal god of the Germans as Mercury, perhaps referring to Wotan.^[9]

Some information about the deities of the ancient Gauls (the continental Celts), who left no written literature other than inscriptions, is preserved by Greco-Roman sources under the names of Greek and Latin equivalents. A large number of Gaulish theonyms or cult titles are preserved, for instance, in association with Mars. As with some Greek and Roman divine counterparts, the perceived similarities between a Gallic and a Roman or Greek deity may reflect a common Indo-European origin.^[10] Lugus was identified with Mercury, Nodens with Mars as healer and protector, Sulis with Minerva. In some cases, however, a Gallic deity is given an interpretatio romana by means of more than one god, varying among literary texts or inscriptions. Since the religions of the Greco-Roman world were not dogmatic, and polytheism lent itself to multiplicity, the concept of "deity" was often expansive, permitting multiple and even contradictory functions within a single divinity, and overlapping powers and functions among the diverse figures of each pantheon. These tendencies extended to cross-cultural identifications.^[11]

In the Eastern empire, the Anatolian storm god with his double-headed axe became Jupiter Dolichenus, a favorite cult figure among soldiers.

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The following table is a list of Greek, Roman, Etruscan, Egyptian, Sumerian, Phoenician, Zororastrian, and Celtic equivalencies via the interpretationes. These are not necessarily gods who share similar traits (as viewed by modern scholarship or readers, at least), and rarely do they share a common origin (for that, see comparative Indo-European pantheons); they are simply gods of various cultures whom the Greeks or Romans identified (either explicitly in surviving works, or as supported by the analyses of modern scholars) with their own gods and heroes. This system is easily seen in the names of the days of the week, which were frequently translated according to the interpretio.

Examples of deities depicted in syncretic compositions by means of interpretatio graeca or romana:

• Jupiter Ammon (terracotta of Hellenistic style, 1st century AD)
• Syncretized figure from the Eastern provinces, perhaps a Genius (1st century BC – 1st century AD)
• Isis holding sistrum and oinochoe (Roman marble, reign of Hadrian)
• Isis, Serapis, the child Harpocrates and Dionysos (relief from Roman Africa, late 2nd century AD)
• Worshipper before Zeus–Serapis–Ohrmazd (Bactria, 3rd century AD)

• Aion (deity)
• Mystery religions
• Honji suijaku, in Japan
• Interpretatio germanica
• Interpretatio Christiana
• Celtic deities
• Proto-Indo-European religion, a reconstructed religion that relates Greek deities to other Indo-European deities
• Shinbutsu-shūgō, a Japanese amalgamation of Buddhist and Shinto deities
• Syncretism
• Three teachings, Buddhism, Confucianism and Taoism as harmonious aggregate in Chinese philosophy.
• Unknown god