CHARLESTON — As workers, politicians and a crowd of onlookers applauded, a huge crane gently lowered a concrete panel into the deck of the $632 million Ravenel Bridge on Friday, closing the last gap in what is now the longest cable-stayed bridge in North America.

“This is a historic day for this historic community,” Charleston Mayor Joe Riley said. He called the soaring bridge with its twin diamond towers “an engineering marvel, ... a bridge of remarkable grace and beauty.”

The bridge, the most expensive ever built in South Carolina, will open to traffic later this year, replacing the two rusting, aging cantilever bridges that cross the Cooper River, linking Charleston and Mount Pleasant along U.S. 17.

Work on the bridge approaches and paving of the eight-lane main span above the shipping channel remain to be completed.

As a chill wind blew in from Charleston Harbor under hazy skies, a crowd of about 100 people gathered in the center of the bridge’s 1,546-foot main span.

A group of six workers in orange safety vests guided the panel into place. Local television stations, their satellite trucks parked just down the bridge, broadcast the moment live.

“We are now officially the longest cable-stayed bridge in North America,” said Bobby Clair, the Department of Transportation engineer overseeing the bridge construction.

The longest cable-stayed bridge on the continent was the Alex Fraser Bridge in Victoria, British Columbia, Canada. The Ravenel’s main span is 20 feet longer. The longest cable-stayed bridge in the world is the Tatara Bridge in Japan with a main span of 2,919 feet, officials said.

“What a great day this is,” Mount Pleasant Mayor Harry Hallman said. “This bridge will make a lot of things happen in this community and the state.”

Then Riley and Hallman shook hands, standing where the bridge crosses the boundary of the two communities.

The bridge’s namesake, former state Sen. Arthur Ravenel, recalled how a new bridge had been discussed for years before financing was finally put in place, in part because of South Carolina’s state Infrastructure Bank.

He noted how he once asked Wade Watson, the project manager for Palmetto Bridge Constructors, the consortium building the bridge, if the job didn’t make him nervous.

He recalled Watson saying that after the challenges of finding the money and getting community approval, building the bridge was a piece of cake.