The World's Tallest Buildings Opened 40 Years Ago Today [PHOTOS]

40 years ago today in 1973, the World Trade Center officially opened for business.

The Twin Towers quickly became an iconic part of New York's skyline, and were featured in countless movies, pictures, and TV shows. They briefly held the title of world's tallest buildings until the Sears Tower in Chicago opened in 1974.

We found some amazing photos from throughout the WTC's history — take a look below.

Groundbreaking for the World Trade Center took place on August 5, 1966.

Some of the buildings' innovations included the high-speed elevators and sky lobbies. They were the tallest buildings in the world at the time, measuring 1,368 and 1,362 feet and 110 stories each.

The Towers were completed on April 4, 1973. Major tenants included Bank of America, Morgan Stanley, and the New York Stock Exchange.

Philippe Petit, a French high wire artist, walked across a tightrope suspended between the Twin Towers in 1974.

George Willig (left) scaled one of the towers in 1977. Daniel Goodwin (right) followed suit in 1983.

On February 26, 1993, the World Trade Center was bombed by terrorists with a van loaded with 1,500 pounds of explosives.

Terrorists attacked the Twin Towers on September 11, 2001, taking down both buildings. The image of the towers burning and collapsing is now an indelible image on the American psyche.

Four years later on September 6, 2005, construction on the World Trade Center Transportation Hub began.

One World Trade Center (also known as the Freedom Tower) is scheduled for completion in Fall of this year. It will be one of the tallest buildings in the Western Hemisphere.