ARLINGTON – For those keeping score, the Dallas Cowboys' future playland has reached another milestone.

Make that a keystone.

A towering crane did the heavy lifting. Workers up high joined sections of steel. And under a blue Sunday morning sky, another of the Cowboys stadium's dramatic arches was complete – its crowning centerpiece set in place.

"It's a big day for us. Another checkpoint along the way," said Jack Hill, stadium construction manager.

Two 1,225-foot-long box truss arches now stretch between grounded concrete abutments to a peak height of 292 feet. The Cowboys tout this as the world's longest single-span roof structures.

Besides making a bold aesthetic statement, the parallel structures will support the stadium's roof and allow for a 160-foot by 72-foot video board to hang above midfield.

Cowboys owner Jerry Jones, along with other team and Arlington officials, watched completion of the first arch in October, with a delighted Mr. Jones hailing the mammoth structures as "the signature of the stadium."

The second arch came together with far less fanfare Sunday. With photographers and reporters there to document, a red crane slowly raised a 110,000-pound section of latticed steel – bearing wind-whipped U.S., Texas, Arlington and Cowboys flags – into place. The final keystone section soon followed.

With the two trusses in place, construction on the stadium roof will quicken, Mr. Hill said, and ground can be cleared for work on its lower bowl.

Begun almost two years ago, the $1.1 billion stadium is about 55 percent complete, he said.

The Cowboys plan to move from Texas Stadium in Irving to their new stomping grounds for the 2009-10 season and will host the Super Bowl there in 2011.

Staff writer Jeff Mosier contributed to this report.