The Athenian artist Polygnotos took enormous care when he painted the dance between Herakles and a satyr on a ceramic wine jar. The red-figured stamnos was created around 430 B.C., probably for ceremonial use -- possibly in celebrations of Dionysus, the raucous god of wine and theater. Today that stamnos lives on a pedestal with protective glass, inside an air-conditioned gallery of the Museum of Fine Arts, Houston.

How did it get there, exactly? And where was it for more than two millenniums?

Was it excavated by archaeologists who carefully recorded its whereabouts? Or by amateurs with brutal shovels and guns?

Was it ever plundered in a war?

Answering those questions with very non-Dionysian precision is crucial to answering another question with real-world repercussions:

Does the MFAH really own that wine jar?

When it comes to the art market, international law is clear and Napoleonic: Owners are guilty until proven innocent.

Laws governing national patrimony vary from country to country, and in many places predate the international laws that apply: 1972 UNESCO Convention and 1995 UNIDROIT accords. In the U.S., Los Angeles-based attorney Thaddeus Stauber explained, "we have some protection for Native American work and work found on federal property. But we (also) have the idea of individual property rights.

"Many countries, though, have laws that anything within its borders belongs to the state -- you may own something as an individual, but you cannot export it."

If an art object was wrongly acquired at any point in its history, its current owner may have to surrender it. At an increasing clip in recent years, such legal wrangling has ensnared institutions, collectors and curators.

Survivors of the Nazi regime and their heirs are reclaiming stolen artworks. This spring, after seven years of litigation, the Austrian government returned five Gustav Klimt paintings to the heiress of Adele Bloch-Bauer; Nazis had stolen them from the family in 1938. One of them -- the luminous portrait of Bloch-Bauer -- sold in June for a stunning $135 million.

Compared to antiquities, the Nazi cases seem simple. Nazis kept records, and it's been less than a century since they seized work. For antiquities, the alleged crimes can date back thousands of years.

For instance, Greece has for decades demanded that the British Museum in London return the famous Elgin Marbles. In the 1800s, while an Ottoman sultan ruled Greece, a British ambassador received the sultan's permission to remove the frieze from the Parthenon. Although the Ottomans were the country's recognized government, Greece claims that the marbles' removal was immoral.

More recent scandals have embroiled American museums. Curator Marion True of the J. Paul Getty Museum, in Los Angeles, is currently in an Italian court, charged with buying illicitly unearthed Greek antiquities for the museum. True and co-defendant Robert Hecht, an antiquities dealer, have denied all wrongdoing.

And in February, the Metropolitan Museum and the Italian government reached an agreement whereby the museum will return 21 objects Rome claimed were illegally excavated.

Legal ownership of works in the MFAH has never been challenged, perhaps in part because its antiquities collection is diminutive for a major museum -- only 389 objects, about half of which are small coins and amulets. By comparison, the J. Paul Getty Museum lists 44,000 objects and the Metropolitan Museum counts 70,000, many of which are monumental -- not only in scale, but also as art and as historical examples.

But the MFAH's collection of antiquities is growing, one object at a time. And each new object requires a clean bill of health stretching back thousands of years, through the muddy haze of wars and looting and even legitimate -- if often undocumented -- trade.

When the MFAH first considered buying the Herakles stamnos, it studied the jar's history with extreme care.

"In today's environment, the collector needs to exercise due diligence," said Stauber, who specializes in financing, governance issues and litigation for charitable corporations. "That includes doing research in depth on provenance."

"Provenance" means "origin" or "source." In the art world, provenance encompasses every known detail of an object's life -- where, when and by who it was made; if it was exhibited or documented in a book or catalogue; when and where it was sold or disappeared.

It's a tough order, given that art theft is older than the Roman sacking of Greece and as current as looting of archeological sites from Peru to Iran. It's the job of the collector, whether private or public, to evaluate the record.

When MFAH curator Frances Marzio suggested that the museum acquire the stamnos with the dancing Herakles, the jar came with a well-established provenance. There are some gaps in its history -- not unusual in an object that is 2,500 years old.

It is attributed to Polygnotos, a vase and fresco painter active in fifth century B.C. His century was that of philosophers and historians, from Sophocles and Plato to Herodotus; it included the playwright Euripides the sculptor Phidias, who created the Parthenon friezes.

Both sides of the red-figure jar salute Herakles, the son of Zeus -- in Greek mythology master of the gods -- and the mortal Alkmene. Herakles' Roman name, Hercules, is synonymous with strength, and he's known for the labors he had to perform.

But this stamnos shows Herakles at play: On one side of the jar, a robed, wreathed and bearded Herakles stands facing a maenad, a young female worshipper of Dionysus who's about to pour a libation from her pitcher into Herakles' extended kantharos (a cup with raised handles). The other side depicts Herakles wearing the skin of the Nemean lion he defeated as his first labor. Herakles plays a double flute while a naked satyr dances and seems to reel in front of him.

The stamnos stands 10 inches tall, and though it is missing its lid, the ceremonial vessel is in very good condition.

"Research indicates that it was probably exported in ancient times and buried in ruins or a grave," curator Marzio said. "Quality vases like this, which were used to mix wine, would most often be only on display in a home, and were often interred with their owners."

According to the Vatican Museum, which also owns a Polygnotos vase, Greek ceramics such as the stamnos were imported primarily from Attica, the area around Athens, to Etruria, a region in central Italy. Stamnoi were "quite recurrent" in Etruscan tombs.

In 1828, a farmer working on one of Lucien Bonaparte's estates in Canino stumbled upon one such a tomb. It was full of clay vessels and jewelry.

Lucien's older brother, Napoleon, had sent him to Tuscany and given him the title of Prince of Canino. But he was "bored out of his mind," says Jasper Gaunt, a specialist in Greek art and curator of the Michael J. Carlos Museum Museum in Atlanta, "and he began to explore the land."

Gaunt estimates Bonaparte's caches of pots at 2,000 to 3,000 among the "tens of thousands of similar jars" that are known.

Lucien Bonaparte was a rare collector, Marzio said. "Everyone at the time wanted the marbles, but he really liked the pots. There are people who say he looted the land," she said, "but you need to remember Italy was not a country then, and Bonaparte did find these objects, which then went all around the world."

Importantly, for the stamnos' provenance, Bonaparte recorded his finds in his memoirs, and scholars of that era also reported the finds.

Sales in the mid-1800s in Paris, London and Frankfurt dispersed Bonaparte's findings to museums from St. Petersburg to the Louvre. The MFAH's Herakles stamnos dropped out of sight sometime later.

It reappeared in the late 1930s in Ugo Donati's Arte Classica gallery in Rome. When Donati's family took refuge from Mussolini, they moved the antiquarian shop to Lugano, Switzerland.

That's where Ferruccio Bolla, a nascent collector, found the Herakles stamnos in 1950. Bolla was 39, and it was the first of what would be many more acquisitions.

Bolla made his antiquities available to scholars and museums. The Herakles stamnos was carefully described and analyzed in the bibles of ancient Greek art -- the scholarly volumes written by Barbara Philippaki (1967) and J. D. Beazley (1968). Other publications, including the exhibition catalog for Stamnoi, presented by the J. Paul Getty Museum in 1980, illustrated and discussed it.

And though the piece received wide public exposure, its authenticity and Bolla's right of ownership were never questioned.

Two years after Bolla died in 1984, the Herakles stamnos sold at auction in Basel. It was offered again in 2000 by Christie's New York. It did not sell, then, but in 2003, Phoenix Ancient Art, a gallery in Lugano, offered the piece to the MFAH.

That fall, Marzio presented the Herakles stamnos to the museum's Collections Committee. She also prepared a brochure for the men attending the MFAH's traditional, men's only One Great Night in November, when patrons Meredith Long and Fayez Sarofim pledged the funds for its purchase. The museum would not disclose the purchase price, but it is valued at $250,000-$350,000, according to Marzio.