New York City ? Two 25-ton steel columns – one bearing signatures of American steelworkers who helped make it – rose Tuesday at ground zero, a milestone in prolonged efforts to build the skyscraper that will replace the twin towers of the World Trade Center.

As construction workers, politicians and architects applauded, a massive crane lifted the first 31-foot-high column, which was painted with an American flag and the words “Freedom Tower,” and set it over steel bars on the southern edge of the tower’s base.

A second column a few feet away carried the signatures of steelworkers and politicians from Virginia, where it spent time at a steel company before being shipped to New York.

By next spring, 27 of the jumbo steel columns to anchor the skyscraper are expected to rise to street level – about 70 feet from the bottom of ground zero.

The 1,776-foot tower, set to open in 2011, is to be the tallest of the five skyscrapers planned to replace the trade center.