World Trade Center's last office tower breaks ground 25 years after 9/11 attacks in NYC

NEW YORK -- A quarter century after the terror attacks of Sept. 11 left a gaping void in Lower Manhattan, American Express broke ground Thursday on its new headquarters, a tiered glass and steel tower at 2 World Trade Center.

The 55-story, two million square foot building with more than an acre of outdoor terraces and gardens is the last commercial development in the footprint of the fallen twin towers of the World Trade Center.

"This has been a long journey," said Lisa Silverstein of Silverstein Properties, the developer of the site since 2001. "This is the capstone for the World Trade Center."

The skyscraper is scheduled to be complete in 2031 and rise 1,226 feet.

Mayor Zohran Mamdani said the project will create 3,200 jobs and inject $6 billion into the city's economy.

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"We are standing today on hallowed ground," Mamdani said.

Officials say the completion of the building will be the final milestone in the commercial buildout of the World Trade Center campus.

"Today is a major milestone towards cementing the status of the World Trade Center campus as a premier location in our city for businesses from around the world to grow and thrive," Gov. Kathy Hochul said. "From the union labor who will build this remarkable tower, to the thousands of American Express employees who will work here for generations to come, 2 World Trade Center will be a shining symbol of the resilience, excellence and opportunity that defines Lower Manhattan."

(ABC News contributed to this report.)