Atlanta is mild and balmy when I arrive, even though it's still early in the year. From the moment I leave the airport, I'm hit by warm air and the non-specific sense of wealth and efficiency that always strikes me when I come to the US. It's particularly strong in Atlanta. From 2000 to 2005, this was the fastest-growing city in America.
A cheerleaders' convention is taking place; heavily made-up pre-teens are wandering around downtown, which isn't quite the historic centre one might expect. A tendency to build and tear down means that characterful old buildings are few and far between. The skyline holds an impressive set of sparkly skyscrapers, but for visitors who have come hoping for something out of Gone with the Wind, they might be a bit of letdown.
Some old friends take me out to dinner. They moved here from New York, and are typical of the young professionals who came to Atlanta during the jobs boom of the Nineties. Two Urban Licks, the trendy restaurant where we eat, is buzzing, crowded and almost too noisy to speak in. The car is parked by a valet. We drink Sweetwater beers. The biggest rotisserie in America – and surely that means the biggest one on Earth? – is on the fritz, so I have crab beignets, and bronzed shrimp on gouda polenta, and cupcakes: rich, spicy, sticky Southern food.
My friends claim to be homesick for New York, but their list of reservations about their new hometown – expensive property, too many incomers, lack of character, too much traffic – seems to sum up the distinguishing features of any city on the up.
The next morning, I wake at seven and watch the televangelist Creflo Dollar preaching on TV. Funnily enough, I'm in Atlanta to pay my respects to a man of God, but it's Martin Luther King Jr and not Creflo that I'm after. The Rev Dollar is wearing a six-button suit and going through the checklist for when you're considering marrying a partner. He's up to number 38. He checks the time on an enormous gold watch. I can't make my mind up about Creflo. On the one hand, he seems to be the incarnation of the holy man with an insatiable pecuniary appetite. On the other, he's a charismatic speaker with great comic timing. I find myself laughing at his jokes and wondering if the coincidence of money and religion is, in fact, objectionable. Should Creflo be paid less than, say, Jimmy Carr?
I head out for breakfast at the Sweet Auburn Bread Company. Martin Luther King Jr was born and raised in the Sweet Auburn district, a walkable neighbourhood of wooden houses that still centres on the Ebenezer Baptist Church, where both King and his father preached. The Sweet Auburn Bread Company is a tiny bakery-cum-coffee shop that serves traditional Southern food. Its chef and owner, Sonya Jones, urges me to try the homemade Georgian peach preserves on my smoked-sausage sandwich. There's also bacon, and buttermilk biscuits. The breads are warm and soft, and baked the way that Southerners like them: a little snap of crispness from the crust and then a warm and pillowy inside.
After breakfast, Chef Sonya brings out the house speciality – her sweet potato cheesecake – and tells the story that made her a local celebrity. When President Clinton came to Atlanta in 1999, he sampled the cheesecake and praised it to the skies. He wasn't wrong: it's unctuous with cheese and a soft pound cake crust, and has a haunting, spicy, orangey flavour of sweet potato.
I ask Sonya whether she favours Clinton or Obama this time round. "It's going to be tough," she sighs, and shows me a poster for each. I ask her to set aside her prior history with the Clintons and pick a candidate on merit. "Forget all the cheesecake stuff," I say. She laughs. "How can I forget the cheesecake? People always ask me, 'Did he pay you for the cheesecake?' I tell them, 'I'm still getting paid for that cheesecake.'"
My next stop is the Martin Luther King National Historic Site, where the great man's memory is honoured in a vast collection that include his grave, his childhood home and a section of the neighbourhood he grew up in.
King shares a final resting place with his widow, Coretta Scott King. Their large marble tomb is ringed with a pool of shallow water. Upstairs, I see King's possessions. When I was a child, my favourite museum exhibit (at the National Maritime Museum in Greenwich) was the jacket that Admiral Nelson was wearing when he died. These items have the same thrilling sense of being intimate with history. There is something worn and human about the heavy suitcloth of MLK's jackets. His shoes. His cufflinks. His shaving powder. His aftershave (the great orator seems to have favoured a splash of Aramis). The conscientiously packed contents of the bag that he took with him on the road. In their totality, the objects bear the faint impress of a single personality: someone stubborn, conscientious, serious-minded. The aftershave adds a reassuringly dandyish touch.
Downstairs, a black paterfamilias admonishes his children for not paying attention to the video monitor that plays the "I have a dream" speech, and then he murmurs along with it as though reciting the Lord's Prayer: "Black men and white men, Jews and Gentiles, Protestants and Catholics." And when it concludes with that rousing shout of "free at last!" he turns to his companion. "Goosebumps every time," he says.
King was only 39 when he was assassinated by James Earl Ray outside a motel in Montgomery, Alabama. The 40th anniversary of this seismic event falls this week. If he were alive today, Martin Luther King would be younger than Margaret Thatcher, George Bush Sr or Nelson Mandela. And yet, King and his assassin were on opposite sides of a struggle that was itself an epilogue to the American Civil War. King understood how much the South was weighed down by its history. In the early days of the civil rights struggle, he set the year 2000 as a realistic deadline for ending segregation. One wonders when he would have thought the country might be ready for its first black president.
Just up the road from the museum, I join a tour party being guided around the house that King grew up in. What's apparent when you visit King's home is that he was not the product of economic hardship. He's not an angry, streetwise hustler like Malcolm X. The detached wooden house is spacious and breathes order and respectability. There's a sense of calm, and a piano in the parlour. The big garden looks out onto a couple of shotgun shacks for poorer families. In this racially mixed neighbourhood, King's family were, if not aristocracy, then Brahmins, the ultra-respectable top tier of a religious hierarchy.
King Jr, like his idol Gandhi, was a middle-class boy who was forced by his conscience into conflict. Standing in his house, I am reminded of a photo in the museum of King being arrested. You might expect him to look defiant, but the look on his face is one of embarrassment. Breaking the law seems to go against his Brahminical sense of respectability.
At the end of the tour, our guide asks us to commemorate Martin Luther King by smiling more. It stimulates the endorphins, she says, and sends out a message of love. It must be St Martin that she wants us to commemorate. King the man was more complex than this. Like Malcolm X, King died as a work in progress. His thinking was still evolving when he was killed. By the year of his death, he had come out against the Vietnam War and was advancing economic views that resemble a variant of socialism. This Martin Luther King is harder for Americans to cheer for.
Still, it was arch-conservative Ronald Reagan who signed the legislation that makes the third Monday in January Martin Luther King Day. Even then, it was not until 2000 that the day was celebrated in every state. Of the 16 people who toured King's home with me, eight were African-American. Later the same day, I visit the house where Margaret Mitchell wrote Gone With The Wind. There are more than 30 people on that tour and every one of them was white.
On reflection, it's not surprising that few black people share that book's nostalgia for the ante-bellum South. But Atlanta seemed full of moments like that. For all its modernity and dynamism, visiting the place you are occasionally shaken up by the sense that you are walking not in history's ashes, but its embers.
STATE LINES: GEORGIA
Population 8 million
Area 7.4 times the size of Wales
Date in Union 2 January, 1788
Flower Cherokee Rose
Motto 'Wisdom, justice, and moderation'
Nickname Peach State
Getting there: Marcel Theroux's trip was booked through lastminute.com (0871 222 5969; www.lastminute.com) which has two nights in Atlanta from £709, including flights with Delta Airlines and accommodation at the four-star Grand Hyatt Atlanta.
British Airways (0844 493 0787; www.ba.com) flies direct from Heathrow.
Eating there: Two urban licks (001 404 522 4622; www.twourbanlicks.com), 820 Ralph McGill Blvd, Atlanta. The Sweet Auburn Bread Company (001 404 221 1157; www.sweetauburnbread.com), 234 Auburn Avenue, NE Atlanta.
Visiting there: Martin Luther King National Historic Centre (001 404 331 5190; www.nps.gov/malu), 450 Auburn Avenue, NE Atlanta. The museum opens 9am-6pm daily, admission free. Free tours of the birth home of Martin Luther King are available on a first-come first-served basis.
Margaret Mitchell's house (001 404 249 7015; www.gwtw.org), 990 Peachtree Street Atlanta. Open 9.30am-5pm Monday to Saturday; 12pm-5pm Sunday. Admission $12 (£6.60) for adults, $5 (£2.80) for children.
More information: www.atlanta.net