CASTELLAMMARE DI STABIA, Italy - Over several centuries, millions of tourists have visited Pompeii to acquaint themselves with the cataclysmic eruption of Mount Vesuvius that began on Aug. 24, 79 A.D. But while it's the most famous eruption site, the ancient Roman city 15 miles south of Naples isn't the best place to gauge the volcano's awesome destructive power.

For that, one should visit lesser-known Herculaneum, which is closer to Vesuvius, or Oplontis and Stabiae, two sites more recently uncovered and still relatively unknown to tourists. In these places, several of which are still being excavated, the eruption's consequences are more visible.

The reason is simple. Pompeii was buried over a period of hours by a prolonged shower of rock, ash and pumice, and then only up to the height of several stories. Nothing was ever built on top of the ruins (the modern city is nearby), which meant that eventually most of the city could be uncovered without superhuman effort.

Today, about 80 percent of Pompeii is open to the sky; it looks like an abandoned city, not a buried one. From many points one can barely see the volcano that put paid to its existence.

It's a different story at Herculaneum, Oplontis and Stabiae - closer to Vesuvius, and between it and the bay. They were buried quickly by a superheated flow of gas, lava and mud that subsequently solidified into dense black rock that not only filled all the buildings but buried them deep underground.

The magnitude of this inundation is dramatically apparent from the terrace of a villa in Herculaneum and another in nearby Oplontis. In 79 A.D., the owners of these luxury pleasure domes enjoyed an unobstructed view of the Mediterranean Sea; today that view is blocked by imposing black walls that were deposited by the flow. The sea could be a hundred miles away.

At Herculaneum and Oplontis, the old settlements are so deep that eventually new towns were built on top. Herculaneum now supports Ercolano, Oplontis is Torre Annunziata.

Nearby Stabiae, a cluster of opulent villas built on the Varano plateau overlooking the bay, has been partially built over but the development is much less dense. The site overlooks the modern town of Castellammare di Stabia. Like Pompeii, Stabiae was buried by volcanic rocks blown from Vesuvius, but to a much shallower depth, perhaps 25 feet on average.

Because much of it lies under modern construction, Herculaneum, originally only a third the size of Pompeii, is less than one-half excavated. An aerial view of the town reveals a massive depression surrounded right up to its rim by houses and apartment buildings.

The same is true at Torre Annunziata, where a villa once thought to have been owned by Emperor Nero's second wife, Poppaea, is the main attraction. Here, too, excavation is constrained by the fact that much of the ruin extends under the modern town.

Stabiae, believed to contain six to eight villas, is a more promising situation for further archaeological discoveries. The villas are much closer to the surface, and recent overbuilding is mainly of individual houses and farms that could be acquired and demolished.

The relatively open site has inspired a proposal that an archaeological park be created that would illuminate a style of living much different from that in Pompeii.

The plan is being pursued by the Restoring Ancient Stabiae Foundation, in which American and Italians are cooperating. Stabiae gets about 1,000 visitors a year; presumably, a major archaeological park would attract thousands more.

Oplontis and Stabiae were not towns like Pompeii and Herculaneum but rather clusters of rambling villas owned by aristocrats like Cicero and members of the imperial family. They might be regarded as the Roman equivalent of the Hamptons or Nantucket, or exclusive gated communities.

Oddly, although some cover thousands of square feet - Villa San Marco in Stabiae, still being excavated, sprawls over more than 140,000 - these extravagent showplaces were built relatively close together. This might seem incongruous, but the villas were designed not for privacy in isolation but to encourage political discussions leavened by entertainment.

They boasted multiple dining rooms with panoramic views of the sea, private heated baths, and lavishly decorated, libraries, gardens and huge colonnaded courtyards. All the walls were decorated with paintings featuring gods and goddesses, women in flowing gowns, and motifs from nature.

Visiting them is a strikingly different experience from strolling through Pompeii. The decorations, especially the wall painting and floor mosaics, are more extensive, more elaborate and better preserved. One of the more striking murals, at Villa Poppaea in Oplontis, depicts a colonnade in recessional space, a visual trick, subsequently lost, that resurfaced in European art during the Renaissance.

The feeling of plutocratic excess is profound in these places; for instance, Villa San Marco has a reflecting pool in its peristyle courtyard almost large enough for Olympic swimming competition.

The other striking feature of these villa sites, aside from the relative lack of tourists, is the way they are hemmed in by modern civilization. Villa San Marco, for instance, bumps against a working farm; one can pet the farmer's horses on the way in.

Villa Arianna (named for Ariadne of Greek myth) overlooks an apartment complex at the base of a steep slope that marks the edge of the plateau. The villa is so close to the edge that part of it has tumbled down the slope. Here, at least, the view to the sea is preserved.

These sprawling palaces were used for only a few weeks a year. They functioned not only as vacation retreats but as meeting places where politicians could gather and deliberate issues of the day far from the cacophony and pressures of Rome.

Places such as Villa San Marco suggest that things haven't changed all that much in two millennia. The rich still luxuriate in seaside mansions whose conspicuous display identifies them as the collateral descendants of the elites who indulged themselves in

otium ludens

- leisurely play - at Stabiae and Oplontis.

"Pompeii and the Roman Villa: Art and Culture Around the Bay of Naples," which opens at the National Gallery of Art in Washington Oct. 16, opens a fascinating window into this world of privilege and material excess. It does this mainly through art, which, along with luxury objects dug out of the volcanic overburden, re-creates - pitch-perfect - the tone of the top stratum of Roman society.