How long did it take to build the twin towers?
The Port Authority of New York and New Jersey began the process of acquiring property for the World Trade Center in late 1964.
Groundbreaking for the World Trade Center took place on August 5, 1966. Site clearing and excavation occurred for the next two years, including the installation of the slurry wall that held back the Hudson River.
In August 1968, steel construction began, with the placement of the first columns of the North Tower (One World Trade Center). Placement of the first columns of the South Tower (Two World Trade Center) followed shortly after in January 1969. The North Tower was topped out on December 23, 1970 and the South Tower was topped out on July 19, 1971. The first tenants moved into the lower floors of the North Tower on December 15, 1970, while the South Tower accepted its first tenants in January 1972.
Full completion of the North Tower occurred during the summer of 1972. The South Tower was largely complete by early 1973, although construction work occurred on the upper floors until as late as 1975 to complete the indoor/outdoor observatory on the 107th and 110th floors. The complex was officially dedicated and opened on April 4, 1973.
Construction on the main World Trade Center superblock concluded in 1975 with the completion of the 9-story 4 World Trade Center in the southeast corner of the plaza. Low-rises of a similar design at 5 and 6 World Trade Center were completed in 1973.
The 360 foot television mast atop the North Tower was installed beginning in 1978, and completed approximately ten months later in April 1979. Additionally, the 22-story Vista International Hotel at 3 World Trade Center began construction in 1979, and was completed and opened by July 1981.
The final addition to the World Trade Center, the 47-story 7 World Trade Center, began construction in 1983 and was completed by 1987.