Trier's location in the Mosel Valley makes it a centre for scenic tours and wine-tasting.
Clawed, and blackened, by the elements perhaps, Porta Nigra has aged like a fine vintage. Built about AD200, this chunky, multi-tiered city gate is the postcard image of Trier, a once-thriving northern outpost of the Roman Empire known as Augusta Treverorum.
Today, while a cluster of European tourists pose for photos in Porta Nigra's shadow, a dozen Chinese peruse a row of nearby pastel-shaded shop-houses. Honing their cameras onto a Euro Shop (where everything costs €1), they listen attentively to their Mandarin-speaking guide.
"Karl Marx lived above there when he was a young child," says Elke, my English-speaking German guide. "Every year we get more Chinese tourists in Trier. And I've noticed a pattern. Groups are dropped off at Porta Nigra, walk through, take a photo of this shop, head down to Karl Marx House (a museum set in his 1818 birthplace). Then they go for dinner at a Chinese restaurant."
I'll delve into Trier's Marxist links later (at a museum, where the Chinese account for a quarter of the annual visitor haul), but, for now, I'm keen to explore a city tucked away in the forested far west of Germany, closer to Luxembourg (46km) than Frankfurt (230km).
First settled by ancient Celtic and Gallic tribes, it was the Romans, under their first emperor, Augustus, who put Trier on the map, about 16BC. Nestled on the right bank of the River Mosel, a tributary of the Rhine (the two waterways meet at Koblenz, 195km north-east), Trier became an important hub of trade, an imperial getaway, a Second Rome – and now bills itself as having more Roman ruins than anywhere else north of the Alps. These relics have earned the city a UNESCO World Heritage rating.
While Elke wears regular dress, other guides cloak themselves in togas and gladiator costumes, and lead visitors around the city's Roman imprints: the imperial baths, subterranean dungeons and cellars, a 20,000-capacity amphitheatre (a venue of Trier's annual Roman-themed Bread and Circuses festival), and the outstanding Trier Archaeological Museum, where eye-catching Roman artifacts, like mosaics, busts, friezes, weapons and ceramics are displayed alongside what's claimed to be the largest Roman gold coin hoard ever unearthed.
Most tours begin at Porta Nigra, the only one of four Roman gates still standing in Trier. Like the city walls, the other sandstone structures were pillaged during the Middle Ages, but Porta Nigra survived because it had been converted into a church and monastery, built in tribute to St Simeon, a wandering Sicilian-born holy man who lived inside the gate for a spell in the 11th century. In 1808, Napoleon's armies destroyed the church.
Leading away from it, Simeonstrasse is the main pedestrianised thoroughfare of Trier's compact, and eminently walkable, historic core, which is laced with photogenic arcades, facades and spires, beneath which lie rows of cosmopolitan al fresco cafes and restaurants.
Just east of Simeonstrasse, I find the massive, airy Constantine Basilica, and its neighbour, St Peter's Cathedral. Constructed in AD310, the basilica, also known as Aula Palatina, served as a lavish imperial palace for Constantine the Great. It's now a rather prosaic Protestant church, but backs on to a flamboyant pink 18th century Rococo palace with pretty floral gardens (a pleasure to amble around).
Built at the same time as its Vatican City namesake, St Peter's is home to the Holy Robe, said to be the tunic that Jesus Christ wore before his crucifixion.
Brought to Trier by Helena, Constantine's mother, the robe is usually hidden away, but makes sporadic public appearances (four in the last 100 years). Its latest showing – in the spring of 2012 – drew an estimated 500,000 Christian pilgrims to Trier.
Such clamour is hard to imagine as I take a breather in the tree-shaded garden of Weinstube Kesselstatt, a restaurant and wine bar facing the cathedral. It serves hearty regional specialities like schnitzel with potatoes and asparagus and sausage with sauerkraut – as well as local hams and cheeseboards, with wines gleaned from Mosel Valley grapes.
Round the corner, I find the sleek Oechsle wine and fish house, where you can sample fresh fish feasts, plus 120 tipples reared from 70 local vineyards, some of which use restored Roman wine presses that have been excavated from the Mosel's banks.
Riesling is the zesty, regional speciality, but there's something for everyone: from dry reds to sweet dessert wines. A tempting offer is Oechsle's €15 taste-all-you-like deal, available during afternoons.
"Of course, you can try them all, but you mustn't," says Oechsle's affable wine manager, Nikolaus Philipps, with a chuckle. "Most people have enough after 20 or 30."
I find it's best to take a Mosel River cruise before (and not after) a visit to Oechsle. On a clear morning, it's a treat to glide along the river. Some excursion boats go as far as Rhine duo Koblenz and Cologne, but the regular two-hour cruises grant a glimpse into the Mosel's bucolic scenery and whet the appetite for deeper exploration.
We pass vineyards tucked beneath rocky cliffs and rolling green hills, antique villages, medieval harbour cranes and a sturdy bridge pieced together by the Romans.
We also keep pace with cyclists pedalling beside the river banks. The Mosel area is one of Germany's major radwandern (bicycle touring) hotspots.
Back in Trier, I visit Karl Marx House. Set over two storeys of a Baroque former burghers' house, the museum tells Marx's story via a series of enlightening exhibits – written, audio and visual.
Born into a middle-class family in Prussian-ruled Trier (his family, incidentally, owned a few Mosel wineries), Marx had developed radical anti-establishment views by his late teens. After falling foul of the Prussian authorities, he fled mainland Europe and settled in England, where his critiques of capitalism – inspired by the pan-European revolutions of the early to mid-19th century – were laid out in the Communist Manifesto and Das Kapital (written with long-time collaborator Friedrich Engels).
The museum gauges the effect Marxist theories had on the 20th century (including on Communist-ruled China) as well as what impact they will have – if any – in the future.
Blessed with a Roman-style bust of Marx, the museum's tranquil back garden is a pleasant place to pause and reflect.
The museum's shop, meanwhile, has a distinct capitalist bent. Alongside serious Marxist paraphernalia, chocolate bars and bottles of wine are coated with red labels featuring a big-bearded Marx.
From the museum, it's a short walk – past a few Chinese restaurants: packed with Chinese tourists – to the Hauptmarkt, Trier's fountain-studded main square. On this fine summer's day, it's alive with espresso and Riesling drinkers, street musicians and fresh produce traders.
Come November and December, I'm told, there'll be Christmas markets, the mulled wine will be flowing and it'll be a chilly, but sehr gut (very good), place to be.
Lufthansa flies from Sydney to Frankfurt from $1708 return; 1300 655 727; lufthansa.com
From Frankfurt, it's a three-hour train journey to Trier via Mannheim, or a 40-minute ride from Luxembourg City; bahn.com
The three-star Altstadt Hotel is a minute's walk from the Porta Nigra. Porta-Nigra-Platz 6; www.friedrich-hotels.de Doubles priced from €101
Park Plaza Trier is a four-star hotel with Roman mosaics and a Roman-themed wellness spa. Nikolaus-Koch-Platz 1; parkplaza-trier.de; rooms priced from €126.
Weinstube Kesselstatt, Liebfrauenstrasse 10; weinstube-kesselstatt.de
Oechsle wine and fish house: Palaststrasse 5-7; +49 651 9917 555
The writer was a guest of the City of Trier