Whenever Elon Musk hypes up his Hyperloop idea—a conceptual transportation system that will whisk passengers to their destinations at speeds up to 700 miles per hour—he makes it sound like the most enigmatic and futuristic idea. Human bodies hurtling through space in the blink of an eye!

However, the underlying technology—air pressure—is actually centuries old. The Hyperloop is a pneumatic system, meaning it uses air pressure to create force, which then moves objects. Musk’s brainchild is still experimental, but the idea has captured the imagination of inventors since the ancient Greeks.

And in New York, actual working pneumatic infrastructure has helped keep the city running for decades, transporting mail, trash, books, and even people. Here’s a look at how this technology has impacted the city.

Air mail … underground

In 1897, New York City’s postal service began building a pneumatic system to transport mail between its 23 post offices. Forget email: This 27-mile-long pneumatic tube network was NYC’s first information superhighway.

The cast-iron tubes were buried four to six feet underground and formed a loop that stretched north to Harlem and south to City Hall, with an extension to Brooklyn. (See a map of the full network here.) As Kate Ascher reported in The Works: Anatomy of a City, air compressors and blowers pressurized the tubes so that two-foot-long canisters, each filled with 500 letters, would shoot through the tubes at speeds up to 30 miles per hour, like mini rockets. (The people who operated the tubes were dubbed “Rocketeers.”)

When the pneumatic mail system opened, New Yorkers were fascinated with the technology. They sent a bible, a copy of the U.S. Constitution, and even a live cat (who, despite the cruel showmanship gimmick, was unharmed) through the system.

At its peak, about one-third of all first-class mail that the city’s main post office processed—about 95,000 letters every day—traveled through the pneumatic system. If this network of air blowers and canisters moving as fast as cars sounds expensive, it sure was. The federal government had to make annual rental payments of 17,000 per mile. This eventually led the postal service to cease pneumatic delivery in 1953.

The proto-Hyperloop

One of the most high-profile pneumatic systems came courtesy of Alfred Ely Beach who, in 1865, patented what he called the Beach Pneumatic Transit. He saw a pneumatic mail system in London and wondered if larger objects could be moved using the same technology. Using his own money, he prototyped a one-block-long tunnel with high-powered fans on either end, which would create enough pressure to propel a railcar. (In the Hyperloop’s case, air pressure is so low that it’s almost a vacuum. A pod magnetically levitates in the tunnel and since there’s no air friction or resistance, the pods can move much faster than they could in open air.)

Beach’s system never advanced past the prototype stage—though people actually traveled on the line—but his proof of concept worked, since the city decided to explore elevated railways for public transportation.

Getting rid of trash at 60 MPH

Roosevelt Island uses a pneumatic system to collect trash. Since 1975, the island’s 12,000 residents—who live in dense multi-family buildings—throw away waste into trash chutes which lead to a trash room in each building with a trap door. (Cornell Tech’s recently completed campus isn’t connected to this system.)

A few times a day, the sanitation department trips the doors, which brings the trash to an underground system of 20-inch wide piles. These whisk refuse away at 60 miles per hour to a centralized facility called the automated vacuum assisted collection system (AVACS). Located on the north side of the island, the AVACS contains centrifugal turbines that spin at high speeds, creating a vacuum that sucks trash into a compactor. (Every day, it collects about 10 tons of waste.) Then, the compactors crush the waste to one-twentieth of its size before it’s trucked off the island—a technique that cuts down pollution and noise since garbage trucks aren’t routed there.

Smaller pneumatic systems have existed elsewhere New York—like at the public library, the Plaza Hotel, and in office buildings—but the technology isn’t just a neat piece of historical trivia. It’s proved to be relevant infrastructure that could help the city run more efficiently. Hudson Yards—the megaproject on Manhattan’s west side—is installing a pneumatic system similar to Roosevelt Island’s to handle trash, recycling, and possibly compost, according to the New York Times. At one point, the High Line considered installing its own pneumatic trash system.

So while pneumatic systems are often out of sight and out of mind, they may also be the future of infrastructure in New York.