We tend to think of the ancient Greeks as enshrined in uniqueness; as influencing, but not influenced themselves by, the cultures that surrounded them. Though there have been fierce attacks on this conception of the Greeks – most notoriously, perhaps, by Martin Bernal in his “Black Athena” – we cling to it all the more stubbornly. After all, our image of Greece, and especially of fifth-century Athens, lies at the heart of how we define ourselves.

We know that mathematics and astronomy were highly cultivated among earlier civilizations, such as the Babylonian and the Indian; even so, Euclid’s geometry and Archimedes’s “eureka” dominate our historical imaginations. American democracy itself, a concept for which we still use a Greek-based term, is invoked as our particular legacy from fifth-century Athens. (Never mind that the Greeks practiced a narrowly exclusive form of democracy, which would have been unrecognizable and abhorrent to us, or that Plato himself despised the rule of the “demos” as one of the baser forms of government.) Writing began in Sumer; the Phoenicians invented the alphabet. But Greeks, as much for our image of them as for their supreme accomplishments, forever defined the golden childhood of our cultural memory.

It comes as a bit of a letdown to realize that this Philhellenism is decidedly overblown. But the process of revision began a long time ago, with Nietzsche and his 19th-century colleagues in Basel, J.J. Bachofen and Jakob Burkhardt. In his remarkable book of 1951, “The Greeks and the Irrational,” E.R. Dodds decisively toppled the cool marmoreal figure of unflappable Greek rationality from its pedestal. Other scholars have been steadily chipping away ever since, not out of perverse revisionism but in order to gain a truer and more nuanced understanding of classical antiquity.

Walter Burkert, born in Bavaria but for some 30 years a professor of Classics at the University of Zurich, is one of the finest and most searching of these scholars. His studies of Pythagoreanism, of Greek cult and ritual, and of ancient Greek religion in general have complicated and refined our sense of the true nature of “the glory that was Greece.” The results, for the nonspecialist at least, are fairly amazing.

His latest book, “Babylon. Memphis. Persepolis: Eastern Contexts of Greek Culture”(Harvard University Press, 171 pages, $22.95), contains five lectures he delivered in Italian, in April 1996, in Venice. The lectures constitute a synthesis of what is now known or suspected about oriental influences on Greek religion and thought. He begins with alphabetic writing itself and proceeds to Homer and the alien elements taken up in his epics, Greek notions of cosmogony, and the influence of Egypt on Orphic cults. He concludes with a brilliant tour de force on Iranian and Zoroastrian elements in Greek philosophy and belief.

The overall effect, far from diminishing Greek genius, is to show just how porous and receptive it was, how consummately it transformed what it had assimilated. “What has often been acclaimed as the first major contribution of the Greeks to world civilizations is in fact a strange mixture of misunderstanding and genius,” he writes. The Greek alphabet provides one example. In Semitic alphabets, vowels are not considered; the letters all signify consonants. But when the Greeks adapted this – from the Phoenicians, a Semitic people – they read the letters in accord with their initial vowels; thus aleph (alpha in Greek) came to be read and pronounced as “a,” rather than as the consonantal glottal stop it denoted in Semitic, jod (which Greeks pronounced as iota) came to be read as “i,” and so forth.

Mr. Burkert’s discussion of “orientalizing features” in Homer is one of the most interesting, and illuminating, in the book. In 1872, the Babylonian epic Gilgamesh came to public attention; not long afterwards, none other than the British Prime Minister William Gladstone “was the first to compare Oceanus and Tethys in Homer’s Iliad with Apsu and Tiamat at the beginning of the Babylonian epic of creation, Enuma Elish.” A fad for finding parallels between Babylonian or Egyptian texts and Homer sprang up and briefly flourished. And though Gladstone’s observations were dismissed at the time, Mr. Burkert shows how very well founded they are.

By a close discussion of the “Deception of Zeus” episode in the Iliad in comparison to the Babylonian epic, Mr. Burkert proves that the Greek name Tethys actually derives from Akkadian Tiamat, so that “here, right in the middle of the Iliad, the mysterious name of the primeval mother comes directly from an Akkadian classic and thus bears witness to its influence.” Though he engages in phonological analysis of both Greek and Akkadian – not the most titillating of topics – Mr. Burkert does so with a surprisingly light touch. We seem to be following the ratiocinations of a lexical sleuth in hot pursuit of his ancient quarry.

If any subject is seen as quintessentially and incontrovertibly Greek, it is philosophy; not merely a “love of wisdom” but a vocation, a way of life dedicated to the quest for truth. Most of the philosophical topics we still grapple with derive from the Greek agenda. Even here, however, Mr. Burkert shows us that the matter is more tangled. Drawing on recently discovered papyri, found as far afield as Ukraine, Crete, and Macedonia, he delineates the subtle, fragmentary, and elusive strands that link pre-Socratic philosophers such as Parmenides to Egyptian beliefs through the medium of Orphism, itself allied with “older Eastern traditions, Akkadian, Hurrite-Hittite, and Egyptian most of all, traditions that are apt to enrich more than to obfuscate our picture of the Greek spirit.”

Mr. Burkert’s last chapter, “The Advent of the Magi,” is one of the best short introductions I know to the maddeningly intricate subject of ancient Iranian custom, languages, and doctrine, especially the history of Zoroastrianism. But I have neither the space – nor the foolhardiness – to attempt to summarize it here. He threads his way through this maze by following the permutations of the word “mage” from its earliest Avestan sources into the Greek language and beyond – a lexical migration that would be dizzying if it were not conducted so clearly.

Mr. Burkert is something of a mage himself; not only a “wise man” and astonishingly learned, but a superb initiator into mysteries gleaned from recondite sources in dozens of dead languages. By bringing these lost or forgotten texts into vivid conjunction, he summons the past to life in all its unexpected intricacy. He shows us that the Greeks, whom we thought we knew, were stranger, and more wonderful, than we could have suspected.