Photos: Building the twin towers

Updated 2:08 PM ET, Mon April 29, 2013
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Ground was broken for the World Trade Center in August 1966. In 1967, the site was cleared for the twin towers alongside the Hudson River in Lower Manhattan. The first tenants of One World Trade Center, the north tower, moved in in late 1970. Fox Photos/Getty Images
Cranes were in position at the excavation site in December 1968. Fox Photos/Getty Images
Storms hovered over the New York skyline as the twin towers of the World Trade Center continued to rise in 1971. A. Vine/Express/Getty Images
Engineers built the towers without masonry, relying on an innovative structural model using a rigid hollow tube of steel columns, shown through a rooftop view in 1971. A. Vine/Express/Getty Images
The Port Authority of New York and New Jersey was responsible for the construction and operation of the World Trade Center, shown circa 1971. Arthur Swoger/Getty Images
Designed to be a complex of seven buildings, the World Trade Center was known for its signature twin towers, shown here a few weeks before their inauguration in April 1973. J Byrnes/Getty Images
In the winter of 1976-77, ice formed on the Hudson River during New York's coldest January in eight years, with temperatures dropping to -8 degrees Fahrenheit, a 40-year low. The twin towers shone in the background. Peter Keegan/Keystone/Getty Images