From the Rockefellers to the Vanderbilts, meet America's outrageously wealthy 'robber barons', a term given to the 19th-century American industrialists and financiers who made fortunes by monopolising entire industries.
As well as hoarding wealth and heading up powerful families, they built some of the most showstopping residences the country has ever seen during the Gilded Age and early 20th century.
Click or scroll through to discover quintessential mansions from the time and the stories behind them....
Rising from relatively humble beginnings, William Rockefeller Jr started his business career as a clerk at just 16 years old. But after joining his brother John D's company, Rockefeller, Andrews & Flagler (which later became Standard Oil) in 1870 his fortune changed significantly.
Within a decade the siblings were among the richest people in the world. William Jr was the first of the duo to build a mansion to reflect his new-found wealth and elevated social status.
In 1886, the Rockefeller mogul paid the equivalent of $4.4 million (£3.5m) in today's money to acquire the Rockwood estate, which overlooks the Hudson River near Sleepy Hollow, New York.
The oil tycoon wasted no time extending the property to 1,000 acres (404.7ha) and transformed the existing house into a splendid 204-room castle.
The second-biggest private home in the US at the time of its completion with 204 rooms, the Elizabethan-style pile cost the best part of $100 million (£78.3m) when adjusted for inflation.
Only the most prestigious designers and artisans were hired for the construction project, including renowned landscape architect Frederick Law Olmsted, who laid out the exquisite grounds (which housed a working farm).
The historic house featured 14 master suites and 15 servants' bedrooms, each grander than the last. The interiors were the handiwork of Ebenezer L Roberts and design firm Carrère and Hastings, Roberts had previously worked on other illustrious homes although sadly died in 1890 before Rockwood was completed.
Suitably grand, the designed spaces encompassed a great hall, library, drawing room, billiard room and other formal rooms for conducting Standard Oil business. Every detail was considered and the home was finished in luxury materials such as marble, oak and onyx.
Following William Jr's death in 1922, at Rockwood, the property passed to his nephew, John D Rockefeller Jr who sold it just a year later. A group of investors swept in and formed Rockwood Hall Inc. purchasing the home and around 800 acres (324 ha). They converted the estate into a country club with a golf course, a swimming pool and other facilities.
But the business floundered during the Great Depression and the mansion and land were bought back by John D Jr in 1937, although sadly he had no use for the sprawling hall anymore and rising debts. By early 1942, John Jr had ordered the demolition of the mansion and all buildings on the grounds except for two gatehouses.
Meanwhile, the richer of the Rockefeller brothers, John D went on the become the world's first billionaire. A frequent visitor to his brother's estate, he was clearly inspired. The wealthier sibling bought land in the nearby Pocantico Hills in 1893 and ended up commissioning his own palatial mansion.
Like Rockwood, the home would overlook the Hudson and be every bit the grand estate. Let's see how he did...
'Kykuit', the Dutch word for 'lookout', rivalled Rockwood in splendour, the 40-room, Beaux-Arts beauty was originally designed as a steep-roofed, three-floor mansion.
But the plans were radically changed by celebrated architect Williams Welles Bosworth, who created a more ornate, six-storey Georgian Revival edifice. Six years in the making, the house was finally completed in 1915.
Needless to say, John D went all out on the interiors, calling upon the services of top interior designer Ogden Codman Jr, who decorated the elegant neo-classical-style rooms with English antique furniture and collections of prized Chinese and European ceramics.
This included Ming dynasty pieces bought from the collection of banker J P Morgan and other ridiculously expensive finery.
John D also equipped his estate with all the latest must-have amenities, including a private golf course and tricked-out coach barn filled with gleaming carriages and cars.
Ultimately, the manse served as home to four generations of the Rockefeller family, with each resident adding to its prestige – particularly John D's grandson, Nelson Rockefeller, who amassed a stunning collection of 20th-century art.
The property was opened to the public following Nelson's death in 1979 and today, visitors can marvel at Andy Warhol paintings, Henry Moore sculptures and a collection of Picasso tapestries, along with the vintage cars and many lavish furnishings.
These are beautifully preserved, as are the manicured Italian gardens.
Coke and steel baron Henry Clay Frick racked up a fortune second only to the Rockefellers, so could certainly afford to go out all on his Manhattan mansion.
And he didn't disappoint. At its completion in 1913, the 61-room Fifth Avenue property was described as the most expensive and sumptuous house in America, with the plot alone costing $76 million (£59.5m) in today's money.
Frick appointed Carrère and Hastings, the firm behind Rockwood Hall's interiors, to design the three-storey mansion in the fashionable Beaux-Arts style.
The brief was for a house that would be “in good taste, and not ostentatious”, and while lavish, the property isn't overly extravagant and embellished. But the contents are another story entirely.
Frick packed the manse with his peerless collections of Renaissance and Rococo furniture, Meissen and Sèvres porcelain and Limoges enamels, and, most notably, one of the finest privately-held collections of paintings in the world, including works by Holbein, Vermeer, Goya and Fragonard.
He even went as far as creating a Rococo-style Fragonard Room to display a famous ensemble of panels by the French artist.
The most impressive spaces must be the cavernous East and West Libraries, with their concave glass ceilings and beautifully carved cornices.
Frick lived in the property for just five years. At his death in 1919, the tycoon gifted the entire manse and all its contents, including the unbelievable art collection, to the American people.
The most deep-pocketed of America's Gilded Age philanthropists, Frick also left $15 million (£11.8m) – the equivalent of $241 million (£188.8m) today – to fund the eponymous art museum, which opened in 1935.
The metal magnate's will included a 150-acre (60.7ha) park and other legacies to boot, amounting to billions in 2022 dollars. Together, they represent the largest bequest in US history.
Aside from the Rockefellers, the other great dynasty of the Gilded Age is that of the Vanderbilt clan, who built more than their fair share of OTT mansions with the money they raked in from shipping and railroads.
Cornelius Vanderbilt II, for instance, ended up erecting the Big Apple's largest and grandest home.
Constructed on the Millionaires' Row section of Fifth Avenue, the ravishing château-style mansion was completed in 1882 and was majorly expanded in the early 1890s.
Cornelius splurged millions on the renovation, hiring 600 artisans to toil away day and night on the huge project.
Done and dusted by 1893, the enlarged property, inspired by France's Château de Blois, featured 130 rooms, including a regal 65 by 50-foot (20 by 15m) ballroom, Louis XIV-style salon and even a Moorish-influenced smoking room.
Elsewhere, the dining room was adorned with paintings by Constable, Rousseau, Millais and other revered artists.
Tragically, Cornelius didn't get to enjoy living in the unparalleled property for long due to his ailing health, which was worsening by the time the revamp was completed.
In 1896, the heir suffered a massive stroke that left him disabled. He lived only a further three years, dying suddenly in 1899 of a brain haemorrhage.
Cornelius' wife Alice remained in the property until 1926. By this time, Fifth Avenue had transformed from a street resplendent with stately mansions to one lined with skyscrapers.
Sold for $108 million (£84.6m) in today's money, the mansion was unceremoniously demolished and the Bergdorf Goodman department store was built in its place.
John D Rockefeller was usurped as the richest person in the world during the 1900s by arch-rival Andrew Carnegie.
Born in Dunfermline, Scotland in 1835, the Scottish-American industrialist spearheaded the expansion of the steel industry in the US, stockpiling a fortune that translates to hundreds of billions in today's money.
Another legendary Gilded Age philanthropist, Carnegie gave away a staggering 90% of his wealth during his lifetime, funding everything from charities to universities. Like the equally generous Henry Clay Frick, the Scottish-born tycoon had humble tastes.
In 1898, he quietly bought 1.3 acres (0.5ha) of land along Fifth Avenue a mile north of the most desirable stretch and asked architectural firm Babb, Cook & Willard to design the “most modest, plainest, and most roomy house in New York”.
Completed in 1902, the 64-room Georgian Revival mansion turned out to be quite a bit grander than the brief outlined, but was certainly roomy at 56,368 square feet (5,237sqm), giving the Cornelius Vanderbilt II house a run for its money.
As this photo of the library shows, the interiors were big on embellishment, with decorative wall panels and ceilings and plenty of plush antique furnishings.
The mansion was also something of a technological marvel. It was the first residence in America to be built around a steel frame, and one of the first to have an Otis lift and central heating.
Another wow-factor feature is the property's private garden, which is the largest in New York. In fact, part of Carnegie's reasoning to buy away from the fashionable area was to ensure there would be enough space for a sizeable backyard.
Carnegie died in 1919, and his wife Louise carried on living in the mansion until her death in 1946 when it was bequeathed to the Carnegie Foundation.
The property was leased to the Columbia School for Social Work from 1949 to 1969. Then, in 1972, the foundation gifted it to the Smithsonian, and the Cooper Hewitt Design Museum opened in the building four years later.
One of the richest self-made tycoons of all time, Henry Ford had already made mega-bucks when he commissioned Fair Lane, his 1,300-acre (526ha) estate in Dearborn, Michigan, not far from where the auto pioneer grew up.
Named after his grandfather's birthplace in Ireland, the property encompassed a farm, a laboratory, an indoor pool and skating house, a bowling alley, a power plant and numerous staff cottages, making it more like a village.
Completed in 1915, the 31,770 square-foot (2,952sqm), 56-room main house was, of course, the estate's star draw.
Designed in part by Frank Lloyd Wright, the rustic manse is a remarkable mix of the Midwestern Prairie School and English manor house styles, with a medieval castle vibe thrown in. It fits in beautifully with the charming naturalistic gardens by Jens Jensen.
Inside, great care was taken in particular with the woodwork, which is of exceptionally good quality. The 29-foot (8.8m) bannister, for instance, was meticulously carved from a single walnut tree.
And the expensive touches didn't stop there, with other luxuries such as marble fireplaces, detailed moulding and parquet flooring, such as those on display here.
Like the other rooms in the house, the library is very traditional in style, as you can see from the Chesterfield sofa, heavy wood panelling, carpeting and so on.
The Fords were said to have been old school in terms of taste, favouring Victorian furniture and decoration over newfangled styles like Art Nouveau or Art Deco.
The auto tycoon died in 1927, and his widow Clara lived in the property until her death in 1950. Stripped of many of its furnishings, the house was then used by the Ford Motor Company as a retreat and place for meetings or social events.
In 1957 it was donated to the University of Michigan. Fair Lane, which was recently restored to look more like it did back in 1915, now operates as a museum.
Nicknamed the King of New York, German-born financier Otto Hermann Kahn was one of the Big Apple's richest people during the Gilded Age and early 20th century.
After his first trophy home, a country manor in Morristown, New Jersey, was gutted by fire in 1905, the banker went on the hunt for another location upon which to build trophy manse number two, plumping for Huntington, Long Island.
Kahn pulled out all the stops, hiring illustrious architectural firm Delano & Aldrich to design a European-style castle, and went on to spend the equivalent of $158 million (£123.8m) on the 127-room extravaganza.
And at 109,000 square feet (10,126sqm) Oheka became America's second-biggest private home upon its completion in 1919, bypassing Rockwood Hall.
Determined his new fantasy property wouldn't succumb to a blaze, Kahn had it built in concrete and steel, making the castle perhaps the first truly fireproof dwelling.
Outside, the grounds were graced with a sunken French formal water garden designed by Frederick Law Olmsted, tennis courts, one of the country's largest complex of greenhouses, stables, orchards, an 18-hole golf course and even a landing strip.
The decadently decorated interiors, especially the spectacular ballroom, the dining room and the library with its secret passageway bowled over the property's many VIP guests.
This included F. Scott Fitzgerald, who partly based the estate in The Great Gatsby on the property, while Orson Welles used photos of Oheka Castle to depict the fictional Xanadu estate in his movie Citizen Kane.
Kahn died in 1934. Several years later the castle was sold, and in 1949 it became the property of the Eastern Military Academy. The school vacated the building in 1979 and it stayed empty for a good few years.
Before it was saved in 1984, painstakingly restored and eventually converted into a luxury hotel, Oheka Castle survived more than 100 arson attacks, a testament to its robust fire resistance.
Edward T Stotesbury was among the most prominent investment bankers of the Gilded Age and early 20th century, and one of the richest people in Philadelphia at the time, with a fortune equivalent to around $3 billion (£2.4bn) today.
In 1916, construction began on Whitemarsh Hall, the financier's breathtaking mansion just outside the City of Brotherly Love. Stotesbury clearly didn't do things by halves.
Beaux-Arts architect Horace Trumbauer was hired to design a stately 147-room manse which, at 100,000 square feet (9,290sqm), would eclipse the White House in size and become America's third-biggest private home.
Dubbed the American Versailles, the glorious neo-Georgian residence was completed in 1921 at an estimated cost of $10 million (£7.8m) or $155 million (£121.5m) in today's money.
The banking executive turned to high-profile landscape designer and urbanist Jacques-Henri-Auguste Gréber to take care of the grounds. The head gardener of Louis XIV of France and the creative mind behind the gardens of Versailles, the outside spaces mimic those at the iconic château.
For the interiors, Stotesbury sourced the finest antiques and artworks from Europe, even roping in an English lord to help him track down the crème de la crème of 18th-century French furniture and English portraiture.
The banker lived a lavish lifestyle at the manse, hosting many a glittering party there and knocking the socks off his VIP guests. After visiting Whitemarsh Hall, Henry Ford declared that it was “a great experience to see how the rich live”.
Following Stotesbury's death in 1938, his wife Eva found she couldn't afford the millions of dollars required annually for upkeep and moved to her Florida estate. In the early part of the Second World War, the empty house was used to store thousands of artworks from New York's Metropolitan Museum of Art
Whitemarsh Hall was sold in 1943 and converted into a laboratory, becoming derelict in the 1960s and 1970s, and was sadly demolished in 1980. Unsurprisingly, it's now considered one of America's biggest architectural losses.
The most jaw-dropping Gilded Age mansion of them all was built for George Washington Vanderbilt II, the brother of Cornelius Vanderbilt II.
Beginning in 1889, over a thousand workers were hired to construct the colossal 178,926 square-foot (16,623sqm) residence on 700 parcels of land totalling 125,000 acres (50,586ha) in scenic Asheville, North Carolina.
The 250-room mansion was designed in the majestic château style by Richard Morris Hunt, the Beaux-Arts architect behind the Statue of Liberty pedestal and New York's Metropolitan Museum of Art's façade and Great Hall.
It was named Biltmore after the Dutch town of De Bilt, where the Vanderbilts originated. Completed in 1895, the final bill for the unprecedented residence would have been equivalent to $1.6 billion (£1.3bn) in today's money.
George W, an avid collector of art and antiques, packed the four-acre manse with sought-after paintings and furnishings dating from the 15th to the 19th centuries.
The pampered heir certainly had a long shopping list, with 35 bedrooms, 43 bathrooms and endless formal reception rooms to decorate.
During its heyday, the property hosted the great and good of American society, from presidents to writers such as Edith Wharton and Henry James.
Following George W's untimely death in 1914, his wife Edith struggled with the running of the vast estate, which had become a major drain on her finances.
Stung by taxes and the cost of maintaining Biltmore, Edith disposed of large swathes of the estate and it was opened to the public in 1930.
These shrewd moves ensured the property stayed in the family, unlike the other Vanderbilt mansions, which were all sold off, and today Biltmore is one of North Carolina's most popular tourist attractions.
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