Six metres below the City of London's newest building, the £1 billion ($1.9b) European headquarters of the financial data and media giant Bloomberg, lie the newly restored and faithfully reconstructed remains of one of London's very oldest buildings: a Roman temple dedicated to a virile, bull-slaying young deity called Mithras.
This "Mithraeum" has been open — free — to the public since early November, and a short sound-and-light show transports visitors back to the third century AD, when the temple was in the heart of Londinium, a prosperous outpost of the mighty Roman Empire, full of foreign merchants and sailors. A wooden writing tablet recovered from the site records that Tibullus owed Gratus 105 denarii for various goods, and is thus the City's earliest financial document.
What the all-male cultists who worshipped and feasted in the temple at that time could never have foreseen is that within another century or two, the Roman Empire would have collapsed, and Londinium would be all but abandoned for half a millennium. There is, these remains seem to suggest, no rule that says cities, cultures and civilisations will inevitably endure.
Eighteen hundred years later, Bloomberg's dazzling new state-of-the-art headquarters now stands, as the Mithraeum once did, in the heart of a seemingly flourishing, cosmopolitan London — a veritable temple to globalisation.
So I ask Michael Bloomberg, the company's founder and chief executive, whether — as Donald Trump's America cools on free trade and international alliances, and Britain prepares to quit the European Union — our own Anglo-Saxon civilisation might also be facing decline. Somewhat to my consternation, he suggests it may be.
"I think it's very worrisome," he says as we sit in a large, open-plan office on the building's sixth floor. "We are in a world where, because of technology, you have to interact with everybody else, and if you try to cut yourself off it's really hard to see how you can thrive. 'Survive' is probably overstating it, but certainly 'thrive'."
Warming to the theme, he tells me he has recently returned from China, where people are proud of their country. They smile while Westerners grimace. "I really am worried about it. I don't want to take anything away from China, but they are ascending, and it's hard to argue that Western Europe, including the UK, and North America, particularly the US, less so Canada and Mexico, are doing the same thing."
It is not just that the US and Britain are pulling up their drawbridges. At various points in our hour-long conversation he laments the breakdown of bipartisanship in America, the lack of civility in public discourse, the disparagement of experts and experience, the pervading culture of blame, the increasing sensationalism of the media, the decline of public health and education, the baleful effect of television and fast food on family life, and the amount of time people spend "playing Angry Birds on their iPhones rather than communicating".
"We're heading towards a world that's not a good one — not a place you would want your kids to grow up in," he says, though he adds, "I'm optimistic in the sense that I still think we can do something about it."
Bloomberg is short, dapper, courteous and in remarkably good shape for a man of 75. Hours before our mid-morning interview he had flown overnight from New York to Luton in his Falcon jet, freshened up at his house in Cadogan Square, then taken the Tube from Sloane Square to Mansion House to preside over the Mithraeum's opening ceremony at 10am.
He is a spectacularly successful businessman who, since being laid off by Salomon Brothers in 1981, has amassed a US$48 billion ($70b)fortune by providing the financial world with instant market data on Bloomberg terminals. He is now the world's 10th richest person, though — monogrammed blue shirt aside — you would never know it.
He has few airs and graces. He has no private office in the new open-plan headquarters — just a desk in a pod like everyone else. Studiously egalitarian, he dislikes titles and insists that even the lowliest of his 19,000 employees around the world call him Mike.
He was also a very successful, three-term centrist mayor of New York. In 12 years from January 2002, he helped it to recover from the 9/11 attacks that destroyed the World Trade Center, steered it through the financial crash of 2008, turned its budget deficit into a surplus and transformed the Big Apple into one of America's safest and cleanest cities.
It's true that he was sometimes seen as arrogant, spent US$260 million on his three election campaigns, and attracted criticism for raising property taxes and supporting a police stop-and-frisk policy that disproportionately targeted minorities. But he also declared war on trans fats, smoking and fizzy drinks, and accepted a salary of just US$1 a year.
Today, Bloomberg has a new role. He is the anti-Trump. In the absence of an obvious Democratic standard-bearer, he has become an — or even the — unofficial leader of the Opposition, using his massive wealth to resist the policies of a president whom he has described as a con man and dangerous demagogue.
Indeed, Bloomberg is everything his fellow New York billionaire is not — a globalist, environmentalist, free trader, supporter of bipartisanship, immigration, gun controls, same-sex marriage and abortion rights. He objects when I suggest he is the President's polar opposite.
"I am what I am. If he wants to go and be on the other side, he would be the polar opposite of me, thank you. I'm a little bit older than him," he quips. Besides, he adds, he and Trump do not disagree on everything: "He's in favour of golf, and I'm in favour of golf, too."
Bloomberg is scathing about Trump. He refuses to call him a businessman, insisting he is a real-estate developer who has never managed more than five people and is worth scarcely a quarter of the US$10 billion he claims.
He laments Trump's failure to assemble a good White House team — "if you don't have a team you don't do anything" — and says he will find it hard to attract good people now because his administration is in trouble. He hopes Trump will abandon protectionism because "we have to have global trade if we're going to provide jobs for the people he says he's going to help and the people who elected him". He does not know what the President stands for because "most of the things he talks about now are 180 degrees the opposite of what he did before he ran for office".
When I ask if Trump has demeaned his office, he replies, "The level of discourse and what's acceptable in terms of veracity and civility had gone down significantly, and it's really worrisome."
Inevitably, the conversation turns to Bloomberg's presidential ambitions. A Democrat-turned-Republican-turned-independent, he was tempted to run as a third-party candidate against Barack Obama and John McCain in 2008. He talks almost wistfully about how he wanted to run last year, recalling that he had employed campaign staff, assembled a brains trust and made commercials before concluding that the electoral rules made it impossible for an independent to win.
But what about 2020? How about seeking the Democratic nomination to take on Trump? The two-time grandfather would be 78 by then, but Bloomberg's mother lived to 102 and he is so robust that he still skis, pilots planes and helicopters, and sometimes flies from New York to London and back in a single day. He opposes Trump's policies "violently" (his word) and is already deploying his fortune to resist them.
As Trump pulls America out of the Paris climate agreement, Bloomberg has rallied the country's governors, mayors and corporate chiefs behind a pledge to meet the accord's emission targets anyway.
As Trump moves to revive the US coal industry, Bloomberg campaigns to close down the country's — and the world's — coal-fired power stations in favour of clean energy. As Trump cools on international alliances such as the United Nations and Nato, Bloomberg seeks to build multinational networks and has taken over the Clinton Global Initiative, which brings together heads of state, billionaires, business titans, Nobel laureates and celebrities each autumn to seek solutions to pressing world problems.
Closer to home, as Trump refuses to tighten firearm laws, despite the recent massacres in Texas and Las Vegas, Bloomberg is financing the gun-control lobby and those few brave politicians who defy the National Rifle Association. He has also taken on the tobacco industry, and spent considerably more on philanthropic causes — roughly US$5 billion — than Trump's entire worth.
"I'm thinking about running for president of my block association," is Bloomberg's first answer (referring to his residents' association in New York), when I ask him about 2020. "I've worked at that for a long time," he replies when I accuse him of evading the question.
He stresses that he is very happy running his business, overseeing his philanthropic foundation and enjoying his family.
But finally he opens the door just enough to make it clear that he has not ruled out a 'battle of the billionaires' next time round — and the chance to become America's first Jewish president. "If God came and said, 'Would you like the job?' I would think it's a wonderful opportunity to change the world."