It could be argued that the elevator was the true catalyst for the early-1900s skyscraper movement. Here, finally, was a way to move people higher and higher, and developers certainly took notice.

By 1850 steam and hydraulic elevators had been introduced, but it was in 1852 that the landmark event in elevator history occurred - the invention of the world's first safety elevator by Elisha Graves Otis.

The first passenger elevator was installed by Otis in New York in 1857. After Otis' death in 1861, his sons, Charles and Norton, built on his heritage, creating Otis Brothers & Co. in 1867.

By 1873, more than 2,000 Otis elevators were in use in office buildings, hotels and department stores across America. Five years later the first Otis hydraulic passenger elevator was installed.

The skyscraper era was about to begin, and in 1889 Otis revealed the first successful direct-connected geared electric elevators. In 1898 overseas business had added to the company's growth, and Otis Brothers merged with 14 other elevator entities to form Otis Elevator Company.

In 1903, Otis introduced what would become the "backbone" of the elevator industry - the gearless traction electric elevator, engineered and proven to outlast the building itself. This ushered in the age of high-rise structures, ultimately including New York's Empire State Building and World Trade Center, Chicago's John Hancock Center, and Toronto's CN Tower.

Through the years, elevators have become more sophisticated and efficient. Otis is a leader in developing computer technology, and the company has revolutionized elevator controls, generating dramatic improvements in elevator response time and ride quality. Innovations in automatic controls have included the signal control system, peak period control, the Otis autotronic system and multiple zoning.

More than 60 of the world's 100 tallest buildings have Otis high-rise equipment. And more than 22,000 Otis mechanics maintain 700,000 elevators, escalators and moving walks worldwide.

March 1902 Willis H. Carrier designs practical system for indoor air-conditioning.

March 1903 Development of high-speed, gearless electrical elevator makes buildings higher than 20 stories viable.

June 1903 New York's Flatiron Building completed.

February 1907 Roland Park Shopping Center completed; the project is the nation's first shopping center with six stores.

February 1908 National Association of Realtors established.

January 1909 Standard Oil's John D. Rockefeller becomes the world's first billionaire.

February 1913 The Woolworth Building opens in lower Manhattan; at 60 stories, it remains the world's tallest building until 1931.

March 1916 Term "Realtor" coined to differentiate between "swindlers" and practitioners exhibiting integrity and competence.

January 1922 Sunnyside apartment complex in Manhattan as one of the largest private rental projects of the time.

January 1925 At 933,000, a peak year for national multifamily permits. Issued permits do not reach this level again until 1950s.

October 1929 Stock market crash triggers the most severe depression in U.S. history.

March 1930 Howard D. Johnson starts first hospitality franchise.

January 1931 At 93,000, national multifamily permits hit desperate low.

February 1931 Highland Park Shopping Village considered to be first mall with storefronts facing inward.

May 1931 Empire State Building opens; becomes symbol of Manhattan skyline and skyscrapers around the nation.

June 1932 Depression continues; 1,161 more banks fail and 20,000 businesses go bankrupt.

January 1946 First hotel management contract is signed by Intercontinental Hotels.