Decadent aristocrats must have to get out of the house occasionally — even if they’re enjoying the sort of luxury that might make an ancient Roman proud. This struck me on my first morning on Ischia, when I woke in my mountaintop manse, the Villa Beatrice, with its myriad portals over the azure seas, then ambled down to my sculpted garden for a dose of Mediterranean sunshine.

Bang on cue, Pietro, the concierge, materialised with a caffè latte and freshly baked marmalade cornetto. From the villa’s lemon grove, we pondered a view that was both seductive and wild: below us on the coast, the fairy-tale Aragonese castle was framed by the sparkling Bay of Naples and the distant, ominous form of Vesuvius.

“Che cosa fa oggi?” inquired Pietro. What’s the programme today?

The answer was that I planned to take part in a venerable Italian tradition — visiting the thermal springs that have lured visitors to Ischia for more than 2,500 years.

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It was the Greeks who first settled on this island, back in the 8th century BC. They became fascinated by the mineral waters that shot from crevices in the earth. They imagined the waters being heated by the hundred-headed monster Typhon, imprisoned underground by Zeus, whose struggles were responsible for the island’s regular seismic shudders.

It was the ancient Romans, however, who developed Ischia’s true potential — as a Mediterranean holiday spot. Aristocrats were already flocking to the crystalline waters of southern Italy in summer, and, in elegant seaside resorts, public baths (thermae) were a central part of social life.

After the empire fell, the baths decayed — until the 18th century, when elegant new spas were built on the same sites and the age-old Ischian tradition was revived as part of the European Grand Tour. Today, I hoped, the baths would provide as vivid a connection to the Romans as Pompeii, across the bay.

My first stop was to seek out the remains of a Roman bath that was still in use, so I headed to Casamicciola Terme, Ischia’s most famous spa town, where ruins lie underneath the Balliazi, a celebrated belle-époque spa.

An attendant led me down slippery steps into what felt like a dungeon; steam fogged my glasses as I stumbled in semi-darkness beneath original stone arches and crumbling columns. From the boiling pools below, someone was using a shovel to gather volcanic fango, or mud — a gluey, brown, mineral-rich paste that is now popular for facials.

The scene upstairs in the Victorian-era Balliazi seemed equally raw. Modern spa culture in Italy — and, indeed, in most of Europe — developed as part of the public-health system, catering to consumptives and those suffering from unfortunate skin conditions. This place had the air of a Siberian asylum, with nurses in white coats slinking through silent, marble-floored corridors.

Obviously, while the medical aspect of the ancient baths was still going strong here, the ambience was nothing Julius Caesar would recognise. In antiquity, health was only one of many

reasons to visit the baths. They were also places to meet, sunbathe, work out in the gymnasiums, flirt, dine and drink the sulphurous local wine.

These days, the spirit of Italy’s pagan ancestors resides most clearly at the Poseidon Gardens, on the western side of the island. It sprawls across 15 acres, with 22 heated pools.

The scale of the operation was bewildering, like a cross between a spa and the Hanging Gardens of Babylon. The complex lay between a mountain and the sea, withthe pools arranged on sculpted terraces, graced by stately trees and flower-filled groves. The centrepiece was a bronze statue of the titular Poseidon, god of the sea, poised to fling his trident at the Mediterranean.

And, on this sunny afternoon, the place was hopping. Europeans of all ages pranced about in robes and plastic slippers. Most of them were Italian, although a good number were from Scandinavia and Germany. Throngs were enjoying their pasta and chianti in swimsuits, while next door, in the massage hall, a small army of patrons were mustering for their facials and manicures.

There was a definite Poseidon protocol, and it took me a while to find my way around. I’d been given a suggested “sequence of baths” (20 minutes at 28C, 10 at 34C and so on) and an inspirational poem: “Take your baths by punctual rule / Not too long, too hot, too cool / Strengthen body, strengthen soul / No more pain is our goal.”

The healthy ideal, apparently, was to start chilly and end up warm. But this was free-spirited Italy, so I began dipping randomly — starting with the largest and most popular watering hole (the Ischia pool, 34C), where fountains poured healing waters over swimmers’ heads as they lolled in the mosaic-covered depths, then trotting over to the smaller, shrubbery-surrounded Aphrodite (30C).

I tried the steamy Apollo (40 C) and the soothing Hadrian (28C), before hitting the tiny Japanese pool and the ice-cold Sauna.

By now, I was feeling like a stewed prune, so I retired to the less exotic Olympic-sized pool (heated to 24C), where I did a few laps, then stretched out on the beach.

The sound of gentle waves mixed with the happy chatter at the cafe next door, where a French group were working their way through bottles of Peroni. At last, I had found a place where the ancient tradition of the baths had come full circle.

The original thermae were full-service complexes, luring travellers from across the empire. And they were famously noisy, even a little chaotic. While the highly strung philosopher Seneca complained bitterly about the din of holidaymakers, vendors and hair-pluckers at the baths, most Romans regarded these visits, with their dubious health benefits, as one of life’s ultimate pleasures. As one nobleman recorded on his tomb: “Wine, sex and the baths may destroy our bodies, but they make life worth living.”

The villa: CV Travel (020 7401 1039, www.cvtravel.co.uk) has a week at the Villa Beatrice (www.villa-beatrice.com), which sleeps 11, from £2,925, villa-only, rising to £5,350 in high season. Both Kirker Holidays (020 7593 1899, www.kirkerholidays.com) and Thomson Holidays (0871 231 3235, www.thomson.co.uk) offer hotel packages to Ischia.

Getting there: airlines flying to Naples include EasyJet (www.easyjet.com), British Airways (0844 493 0787, www.ba.com) and BMI (0870 607 0555, www.flybmi.co.uk).

Ferries run every hour or so from the Molo Beverello, in Naples, to the main port of Ischia (£13.50, one-way), which makes the island an excellent day-trip option from the city. Crossings take about 45 minutes.

Further information: the Poseidon Gardens are south of Forio.

A full day ¤costs £22, an after- noon £18; towels and lockers are extra (www.giardiniposeidon.it). For more details of the island, visit www.ischiaonline.it.

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