It’s 70 feet tall, 220 tons and the city’s oldest artifact — but many New Yorkers don’t know it exists.

Cleopatra’s Needle, a 3,500-year-old obelisk from Ancient Egypt, survived a voyage to Central Park more than a century ago and has been a park treasure ever since.

Nestled behind the Metropolitan Museum of Art, the ­hieroglyph-covered column was commissioned by one of Egypt’s most powerful pharaohs and reigns as among the last of its kind.

“It’s our oldest inhabitant,” says Dr. Bob Brier, a renowned Egyptologist at Long Island University’s C.W. Post Campus in Brookville, LI.

“When it was erected, everyone went bananas,” he adds. “Then it was forgotten. Trees grew up around the knoll and obscured it. People just stopped thinking about it.”

Still, Brier says the artifact’s history has enough twists and turns to make a Hollywood film.

Erected in Heliopolis around 1450 BC, the obelisk was toppled centuries later by Persian invaders. It was buried in the dust for 500 years more until the Romans snatched it for ­Julius Caesar.

Now the Central Park Conservancy is embarking on a $500,000 project to clean and preserve the monument — ­using lasers to wipe away ­decades of dirt and pollution.

“There was a recent article about the obelisk, and the writer said it’s boring,” says Brier, who visits the monument every month. “He’s dead wrong. The obelisk is an engineering achievement. It’s an ancient skyscraper.”

Despite its nickname, Central Park’s obelisk wasn’t made for Cleopatra, but for the Napoleon of Egypt.

Thutmosis III amassed the greatest empire in Egyptian history during his 54-year reign. The pharaoh came to power in 1479 BC and claimed to have conquered more than 300 cities from Syria to Sudan, leading his army from a chariot sheathed in gold.

Thutmosis was also a prolific builder, commissioning dozens of temples and obelisks.

To celebrate his 30th year of rule, the pharaoh asked for a pair of pillars to flank the sun temple in Heliopolis — a feat that sent thousands of workers south to the Aswan quarry to cut each monument from a ­single piece of red granite.

While Thutmosis was the brain behind the obelisks and inscribed them with his name, two other kings later seized them and added their own self-serving hieroglyphs to the four sides.

Pharaoh Ramesses II, who reigned from 1279 to 1212 BC, inscribed his praises and left little room for Osorkon I, who crammed his moniker on a lower edge.

The monuments towered above the Nile for more than 1,000 years, until Persians raided the city and toppled them. The obelisks may have burned in the invasion and eroded from spending hundreds of years in the sand.

The obelisks stood again around 12 BC, when Roman conquerors uprooted and moved them to Alexandria. The artifacts were placed then at a Caesarium, a temple honoring Julius Caesar.

After the collapse of the ­Roman empire, and even the fall of the Caesarium, the obelisks still stood. At some point — no one’s quite sure by whom — they were given their nickname: Cleopatra’s Needles.

“Thutmosis’s pair of obelisks quietly faded into the scenery, their presence taken for granted by the Alexandrians,” wrote Martina D’Alton in a 1993 book on the obelisk.

“The obelisks remained ­unperturbed . . . greeting incoming ships and witnessing the departure of obelisks and other treasures bound for distant shores.”

By the 19th century, Europe coveted Egyptian artifacts. England was offered one of the Thutmosis columns in 1801 as a gift for helping Egypt oust Napoleon.

It wasn’t erected in London until 1878, however, after a hazardous journey that cost the lives of six men.

That year, the United States became determined to get an obelisk of its own.

America missed its first chance at an obelisk in 1869 at the opening of the Suez Canal.

Bankrupt and beholden to European creditors, Egypt ­offered US officials the ancient pillar “not out of generosity and friendship but out of desperation,” Brier writes in his 2013 book, “Egyptomania.”

The offer was ignored — ­until New York was overcome with obelisk envy at the sight of London’s gem.

That’s when William Henry Hulbert, editor of The New York World newspaper, and E.E. Farman, the American consul-general in Cairo, launched a public campaign to obtain one.

Egyptian representatives promised Farman an obelisk several times before, and this time he asked for the offer in writing. Under a new contract, Farman made sure the precious relic would go specifically to New York.

In 1879, newspaper headlines declared obelisk victory. Railroad mogul William Vanderbilt covered the obelisk’s transport. Now America only needed a man for the daunting feat of bringing it home.

Henry Gorringe, a decorated Navy commander, stepped forward. At the time, the largest object to sail in the hold of a ship was a 100-ton cannon heading from England to Italy, Brier writes. (London had towed its obelisk.)

Gorringe’s team carefully lowered the obelisk with a cable amid scores of protesters. They slid it into an 83-foot-long wooden box, which was rolled with cannonballs onto a vessel bound for Staten Island.

The obelisk set sail on June 12, 1880, and reached New York a little over a month later. But the treacherous journey wasn’t over. It took another five months for the artifact to reach Central Park.

First Gorringe hauled the obelisk’s 50-ton pedestal to 51st Street and pulled it to the park with 32 horses.

The monument, meanwhile, was towed up the Hudson River to 96th Street on pontoons. Gorringe built a special rail track to move the obelisk through the city at a rate of only one block per day.

As Cleopatra’s Needle inched toward its new home, New York was enraptured in a wave of Egyptomania.

When the obelisk’s cornerstone was laid at Central Park’s Graywacke Knoll, close to East 81st Street, at least 9,000 Free­masons marched up Fifth Avenue to commemorate it with a ceremony.

New York merchants, including a needle company, doled out trading cards in honor of the artifact, showing the Queen of the Nile threading not a needle, but an obelisk.

A candy stand trailed the monument on the voyage to its new home, while another merchant sold “Cleopatra Dates” in an obelisk-shaped box, according to D’Alton. Some restaurants even stirred up “Obbylish” cocktails.

“When the obelisk was erected, ladies wore mechanical lead pencils around their necks in the shape of the obelisk,” Brier told The Post. “People were going crazy.”

On Jan. 22, 1881, thousands of New Yorkers gathered to see the obelisk assembled — two years after its journey from Alexandria.

Before it was erected, a time capsule was buried under its base with documents including the 1870 census, a copy of the Declaration of Independence, Webster’s Dictionary and a small box from Hurlbert. Its complete contents are unknown.

In 2011, the obelisk returned to the spotlight when an Egyptian official accused New York of neglecting the ancient structure and threatened to take it back.

In a letter to Mayor Michael Bloomberg, Zahi Hawass, secretary-general for the Supreme Council of Antiquities, fumed that the obelisk was “severely weathered over the past century and that no efforts have been made to conserve it.

“Recent photographs that I have received show the severe damage that has been done to the obelisk,” he wrote, “particularly to the hieroglyphic text, which in places has been completely worn away.”

The Parks Department and Central Park Conservancy ­rebuffed Hawass’ claims, saying the obelisk’s damage stems from being engulfed in sand centuries ago.

Still, park honchos ordered a “weathering study” shortly after the scathing letter. And a conservation project began this spring.

Bartosz Dajnowski — an Illinois-based conservationist who also restored the George Washington statue at Federal Hall on Wall Street — is cleaning the obelisk with lasers before repairing cracks and covering it with protective coating.

The laser’s infrared beam is set to a distance of 1,064 nanometers and hits the soot but not the ancient granite, Dajnowski told The Post. The pulse lasts about 100 nanoseconds, or 1 billionth of a second.

His three-man team’s meticulous method allows for the scrubbing of 10 square feet an hour.

“The legibility of the hieroglyphs will significantly improve,” Dajnowski said. “The dark deposits are visually distracting and camouflaging some of the hieroglyphs.

“Once the stone surface is evenly clean, the details . . . will be naturally highlighted by the sun, and the shadows cast inside the carvings will make them more legible.”

Conservancy officials say the project won’t reveal any secrets, but rather preserve the obelisk for the decades to come.

Brier, who has studied the artifact for 25 years, hopes to get on the project’s scaffolding.

“Obelisks were almost always one piece, but the tip of our obelisk looks like it was refurbished,” he said.

Perhaps Cleopatra’s Needle has one more mystery to be solved.