During the Gilded Age in America, anything seemed possible.

Skyscrapers popped up in New York, illuminated by newfangled electric lights.

And in South Florida, Henry Flagler built a railroad over the ocean.

Sunday marks the 100th anniversary of Flagler’s Jan. 22, 1912, inaugural trip to Key West via a 128-mile extension — about 19 miles of it over water — of the Florida East Coast Railway.

The extension has been praised as “something beyond anything that had ever been attempted in America before,” said FEC company historian Seth H. Bramson. The anniversary will be celebrated from Palm Beach County to the Florida Keys.

WLRN-TV will air “A Century in the Sun: Henry Flagler and the Making of Modern Florida,” at 8 p.m. on Jan. 22 and 10 p.m. on Jan. 27.

Slices of the actual track, spikes and tools used to build the extension are on display at the Florida Pioneer Museum in Florida City, along with photos of 25 postcards touting the construction of the extension.

The Key West Art and Historical Society’s Custom House museum features a truncated replica railcar. In the windows, footage plays of a trip over the extension so museum-goers can experience what it felt like to be a passenger traveling on the Over-Sea Highway.

“It was such an amazing feat that you could actually build a railway over the sea,” said Claudia Pennington, executive director of the Key West Art & Historical Society. “And it really says something about people in the 20th century — that if you could dream to do it, you probably could.”

The task took eight years, up to 10,000 workers, and $50 million to complete, Bramson said. It connected Key West, then Florida’s richest, most populous city, with the mainland.

Though Key West was a playground for the wealthy, Florida in the late 19th and early 20th centuries was barren from Palm Beach to the southern tip of the mainland. In 1895, only nine people lived along the Miami River, according to that year’s census, said Paul George, a historian at Miami Dade College.

But that was before Flagler’s railroad chugged its way down the east coast of Florida.

As the oil tycoon laid tracks down the coast, developments sprung up. Soon after his railroad passed through Miami in 1896, the area became an incorporated city with close to 800 residents, George said.

“Henry Flagler was really the preeminent developer of Florida,” he said. “It was a young, raw state, and he put so much investment into its east coast, and really helped catalyze its development.”

Flagler’s sights turned to Key West as construction of the Panama Canal began, though he contemplated the extension, which began in Homestead, as early as 1891, George said. Flagler began purchasing the land for the extension in 1904, and the first shovel-full of earth was moved in 1905, Bramson said.

Laborers were brought in from as near as Cuba and as far as Sweden. Concrete that would harden under water had to be brought in from Germany.

Before 1925, the extension was popular and successful, Bramson said. About three passenger trains and two freight trains made their way to Key West every day, he said.

But soon, the Great Depression would hit America — and the FEC Railroad. The company declared bankruptcy in 1931. Traffic on the railway waned.

Then the monstrous Labor Day Hurricane of 1935 tore across Florida, devastating the state. The extension was destroyed in the disaster, and the company, barely able to afford its gas bills, could not rebuild. A highway was later built on railway the right-of-way, with bus service to and from the Keys.

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