There may be no single invention that shaped the modern city as much as the elevator. But the elevator, of course, is not a single invention. It's a series of innovations going back hundreds of years and continuing now and into the future. Otis Elevator Company, founded 160 years ago today, quickly became, and remains, one of the largest elevator companies in the world thanks largely to Elisha Otis, who invented the elevator safety brake in the 1850s. The elevator safety brake made passenger elevators feasible, but many other good ideas, built upon each other over time, enabled cities to push continually skyward. Here are nine — some, but not all of the most important. Elevator Safety Brake Otis' invention, for which he received this patent in 1861, virtually eliminated elevator falls. The device relied on a set of loaded springs that would automatically press downward-facing hooks into upward-facing metal teeth on the sides of the elevator shaft if tension on the rope was released. After Otis demonstrated the brake at the 1854 Crystal Palace Exposition — by having an associate cut the rope while he was on the platform — sales skyrocketed. But more importantly, now that people didn't have to climb so many stairs, tall buildings started to pop up in cities. "That was really the beginnings of not only the Otis Elevator Company, but also the usage of elevators in a big way for passengers, and really enabled the modern city," says Daryl Marvin, Director of Innovation at Otis. Top photo: peering upwards inside the Burj Khalifa's elevator shaft, the tallest in the world. Photo: Flickr/mknobil Lower image: Wikimedia/US Public Domain

Electric-Driven Elevators Inventor Werner von Siemens — yes, the founder of Siemens — is credited with the first elevator with an electric motor, but its adoption wasn't widespread until the first part of the 20th century, when the grid was broad enough that electricity was a reliable source of power, says Marvin. Formerly, hydraulic lifts, like the one pictured here, run by steam or oil, drove the cable-winding cylinder. Patent illustration: U.S. Patent and Trademark Office

Automatic Doors Safety is one of several trends in the history of elevator development, says Marvin. In 1944 Joseph Giovanni of United Elevator Service patented a sensitive door bumper as a way to automatically stop when the elevator door hits an obstruction, say, the wayward limb of a passenger. But safety doors didn't stop there. Elevator companies like Mitsubishi Electric have since incorporated infrared and ultrasound sensors along with pressure-sensitive safety edges. Patent illustration: U.S. Patent and Trademark Office

Microprocessor-Controlled Elevators Another factor driving innovation is efficiency. In 1979, Otis introduced the Elevonic 101 (pictured), which used a TI-99 microprocessor to control where the elevator stopped and when. But it did more than optimize routes; it also automated stops, starts, and the elevator's speed, and further reduced the need for dedicated elevator operators. "[The operators] were, in the early days, doing more than pushing buttons," Marvin says. "In most cases, they had a lever they were pulling on that would change the speed ... and then they would be landing the car with their own skill." Photo: Courtesy of Otis Elevator Company

Sky Lobbies The sky lobby isn't an elevator. It's not even a part of an elevator, and it's not patented (though a system for multiple sky lobbies is). But it's still an important innovation in elevator history, one that helped enable new, super-tall buildings like the Nina Tower in Hong Kong. Like other sky lobbies, the one in the Nina Tower (pictured) is located partway up the building. Passengers who need to get to the upper floors first take a high-speed elevator directly to a staging floor. From there, they transfer to another elevator for the upper reaches. It may sound like a hassle, but it's based on sophisticated passenger flow models. "The analysis all shows that this is a much more efficient way of servicing the building than if you had elevators that tried to get to every floor," says Marvin. Photo: Wikimedia/Baycrest

Double-Deck Elevators Like sky lobbies, double-deck elevators are designed to optimize human flow. By stacking two cars on top of each other — one for odd floors, one for even — elevators can carry twice as many people without adding to their overall footprint. As a result, they offer a reduction in the amount of unrentable core space dedicated to systems like utilities and elevators. "Without that it really would not have been very cost effective to go to the size buildings that we go to today," says Marvin. Photo: Wikimedia/Peregrine981

Compass Destination Entry More recently, Otis has experimented with software solutions to passenger flow. In 2005 the company introduced Compass, a new interface that allows users to select the floor they need before they step onto the elevator. Then the system evaluates all the current requests, selects the best elevator for that passenger, and directs her to it. "It also allows the elevator to be significantly more efficient, in how it services the passengers and gets the passengers to their destination," says Marvin. "We estimate it’s up to 20 to 40 percent faster than the conventional system." Photo: Courtesy of Otis Elevators

Regenerative Drive Also in 2005, Otis introduced regenerative drive on its elevators. But this wasn't an entirely new concept; more than a hundred years prior, Schuyler Wheeler included a system "in which the energy developed or expended by the descent of the material is utilized to supplement the electric energy in the working system or circuits" in his patent for an electric elevator. Both versions work somewhat like a hybrid car when it brakes. As the elevator descends, Otis' ReGen system uses that kinetic energy to generate electrical energy, releasing it into the building's grid. Patent illustration: U.S. Patent and Trademark Office