The sprawling warehouse, which looks big enough to double as an airport hangar, is unofficially known as the “robot highway.”

Inside Amazon’s Denver, Colo., “sortation center,” an army of orange robots –– each one about the size of a large suitcase with a small conveyor belt on top –– glides across the concrete floor, picking up and then delivering packages to one of hundreds of chutes that organize each item by Zip code before they’re shipped to customers.

Though largely unknown to the outside world, the robots, known as Pegasus, have already logged more than 1.5 million miles of driving, according to an Amazon blog post describing work inside the warehouse. (Amazon CEO Jeff Bezos owns The Washington Post.)

Amazon unveiled Pegasus during the keynote session at its first-ever re:MARS conference in Las Vegas this week, devoted to, in Amazon’s words, “Machine Learning, Automation, Robotics, and Space.” It was there that Amazon revealed that the company already has 200,000 robots working at dozens of distribution facilities around the world.

“We sort billions of packages a year,” Brad Porter, vice president of robotics at Amazon, said, according to GeekWire. “The challenge in package sortation is, how do you do it quickly and accurately?

“In a world of Prime one-day [delivery], accuracy is super-important,” Porter added. "If you drop a package off a conveyor, lose track of it for a few hours — or worse, you mis-sort it to the wrong destination, or even worse, if you drop it and damage the package and the inventory inside — we can’t make that customer promise anymore.”

Amazon said they have 40 sortation centers around the world, though their Pegasus technology is operating in only a small number of those. The company said it plans to introduce the machines to more centers.

Despite being home to about 800 wheeled robots, the warehouse relies on human workers, according to Amazon. Asked how many workers are employed inside sortation facilities like the Denver warehouse, Amazon said it’s difficult to obtain precise numbers, which vary, depending on the season and location.

The company said it’s also difficult to reveal the number of workers employed inside warehouses without robots.

Amazon said the company is still hiring human beings for centers where robots are operating and will continue to do so. Human jobs range from area managers and maintenance technicians to safety engineers and “amnesty workers,” who are trained to go on to the floor to fix a robot or pick up packages that may have fallen on the ground.

The Denver “sortation center” is managed by five “flow control specialists” who rely on software to oversee inbound and outbound packages, the company said.

The delivery process begins when a robot arrives at a station where a human “associate” scans a package and places it on top of the machine, according to Amazon. Once the robot takes off, following a programmed route, on-board cameras help the robot avoid obstacles en route to a chute, a journey that takes about two minutes.

The busy traffic is monitored by the flow control specialists, who can access real time information about the fluctuating volume of packages moving through the building using Kindles, according to Amazon. The workers can identify congestion areas in the warehouse or spot robots that aren’t functioning properly, Cathryn Kachura, a “flow control specialist” who refers to the machines as “her babies” in a video produced by Amazon in which she discusses her daily responsibilities.

“If you had told 10-year-old me that my job would revolve around robots every day, there’s no way I would have believed you,” Kachura said.

Amazon plans to continue adding robots to other U.S. sortation centers this year, but it isn’t the only company to offer a glimpse of robots sorting packages inside a warehouse.

In March, Boston Dynamics released footage of a wheeled emu-like robot gliding across a warehouse floor with ease, demonstrating its ability to pick up and move large boxes using what appear to be suction cups at the end of a long neck.

At six feet tall and weighing 231 pounds, the machine, known as “Handle,” was designed to carry up to 33 pounds while maneuvering in tight spaces, according to the company, The robot first appeared online, though in a different form, about two years ago.