The iconic Twin Towers through the years?

World Trade Center, 2001
It's a day that will forever be remembered. Smoke and debris cover what once was the World Trade Center in the aftermath of the 9/11 terrorist attack on September 14, 2001.

World Trade Center, 2001
A lasting image of the World Trade Center: The Twin Towers are seen on a sunny summer day in July 2001, less than two months before the 9/11 attacks.

World Trade Center, 1998
Aerial views of Lower Manhattan and the World Trade Center in 1998.

World Trade Center, 1975
On September 11, 2001, the New York City skyline dramatically changed. To commemorate the 9/11 attacks, take a look back at the iconic Twin Towers through the years ... Here is an aerial shot of Lower Manhattan with the buildings finally complete in 1975 after years of construction. In the foreground, landfill is worked on to create what would eventually become Battery Park City. The World Trade Center site officially opened to the public on April 4, 1973. At the time, the two 110-story towers, designed by architect Minoru Yamasaki, became the world's tallest buildings.

World Trade Center
A worker stands on the top of one of the unfinished towers with the Empire State Building looming in the distance.

World Trade Center, 1970
No fear of heights here! Construction workers are seen on the top floors of the World Trade Center.

World Trade Center, 1970
Construction workers put the finishing touches on the top floors of the Twin Towers during the final stages of construction.

World Trade Center, 1970
A view of the progress of the World Trade Center site during its construction in 1970.

World Trade Center, 1969
The progress at the World Trade Center site in 1969, where a foundation and part of one of the towers is in place.

World Trade Center, 1968
Workmen guide a 34-ton steel unit into place at Greenwich and Fulton Streets.

World Trade Center, 1967
A seven story high reinforcing cage, weighing almost 25 tons, is lowered into the ground on Liberty Street at West Street.

World Trade Center, 1969
A south looking aerial image of the Twin Towers during construction in 1969.

World Trade Center, 1966
On August 5, 1966 construction officially began. Here is a photograph taken that year of the location of the future World Trade Center along the Hudson River.

World Trade Center, 1968
A 1968 aerial view of the site where the World Trade Center was built.

World Trade Center, 1967
All but a handful of buildings in the eight block area of construction are already taken down in this shot, snapped in 1967, looking northwest from the corner of Greenwich and Liberty streets toward Vesey and West Streets.

World Trade Center, 1967
The Liberty Street Ferry, seen here in 1967, had to be partially demolished to allow for construction of the World Trade Center.

World Trade Center, 1967
Here is a view of the World Trade Center area under construction in 1967. Pier foreground, seen in the center, holds reinforcing circles to be used for the building process.

World Trade Center, 1977
Daredevil! George "Human Fly" Willig climbs up the South Tower of the World Trade Center on May 26, 1977.

World Trade Center, 1964
Though the idea for the New York City landmark was first proposed in 1946, it was Governor Nelson Rockefeller, who looks at a model of the World Trade Center in 1964 with its architect, Minoru Yamasaki, that helped make the dream a reality. Yamasaki was the one who came up with the plan to have two towers, later known simply as the "Twin Towers."

World Trade Center, 1970
Here, another aerial shot shows the World Trade Center during construction in 1970. By the time they were finished, the Twin Towers were the tallest buildings in the world.

World Trade Center, 1968
The first steel fountain is placed during the World Trade Center construction in 1968.

World Trade Center, 1969
A photo of a steel stockpile used in the construction of the World Trade Center at the Greenville Yards in Jersey City, New Jersey.

World Trade Center, 1967
Here, a general view shows the beginning of construction on the World Trade Center in Lower Manhattan. Ironically, this 1967 shot looks eerily similar to how the site looked following the 9/11 attack.

World Trade Center, 1983
Onlookers watch Daniel Goodwin from above and below as he scales the World Trade Center in 1983.

World Trade Center, 1967
Commuters go about their day as they cross Vesey Street during construction on the World Trade Center in 1967.

Boycotting World Trade Center, 1962
Not everybody, however, was on board for the massive undertaking. Oscar Nadel and his wife sign a boycotting World Trade Center petition outside his store Oscar's Radios, located at 176 Greenwich Street in Lower Manhattan. The 1962 "Radio Row" protests included having a coffin lying in the streets with a sign that read, "Here lies Mr. Small Businessman. Don't let the Port Authority bury him."

World Trade Center, 2001
With Governor Pataki (l.) and New Jersey Acting Governor Donald DiFrancesco (r.) looking on, Larry Silverstein (c.) signs on the dotted line to complete the $3.21 billion deal in which the Port Authority of New York and New Jersey hands over the World Trade Center Twin Towers and buildings 4 and 5 to Silverstein Properties for 99 years. Standing from left are Port Authority Vice Chairman Charles Gargano, Port Authority Chairman Lewis Eisenberg and CEO Peter Lowy of Westfield America, a partner in the deal.

World Trade Center, 1999
Austin J. Tobin was the executive director of the Port Authority of New York from 1942-1972. After his death, the outdoor plaza of the World Trade Center, seen above, was named after him.

World Trade Center, 1993
On February 26, 1993, a car bomb tore apart the bottom level of Tower One of the World Trade Center. While miraculously only 6 people were killed in the explosion, smoke quickly filled the tower and many were injured during the mass evacuation of the building. Here is a photo of police rescue efforts after the explosion.

World Trade Center, 1983
Climber Daniel Goodwin successfully scales the North Tower of the World Trade Center on Memorial Day, May 30, 1983. Goodwin made the climb after having already climbed the Sears Tower, Renaissance Tower and John Hancock Center.