A milestone was marked in Philadelphia Monday as a newly constructed metal building became the City of Brotherly Love's tallest - and the highest in the United States between New York and Chicago.

The final beam was placed on the steel building that will become the new Comcast Center at 17th and John F. Kennedy streets.

Pressing a red power button on a giant remote control, Ralph Roberts set in motion - symbolically - the ascent of a steel beam to the top of Comcast Center.

It's the last beam in what is now Philadelphia's tallest steel building - or structure of any sort.

The Comcast Center will be 975 feet tall, 30 feet taller than One Liberty Place, which has been Philadelphia's tallest building.

The project broke ground in January 2005, and with the steel building frame already in place, it is scheduled for completion in spring.

Roberts is the 87-year-old founder of Comcast, which is leasing nearly 90 percent of the building for the cable giant's new headquarters.

When completed, the 975-foot commercial metal building will be the tallest skyscraper between New York and Chicago.

The ceremony Monday heralded the hoisting of the beam to the highest structural point of the steel building.

The beam held a small bronze statue of William Penn. Until 1987, developers kept steel buildings shorter than a statue of Penn atop City Hall.

But all eyes are on the newest skyscraper - a steel building that will transform the Philadelphia skyline and, some believe, give this old city a renewed vitality.

"We have spent an awful amount of time improving the quality of life of people who live in the neighborhoods but they have to have a place to work," Mayor John Street said.

The Comcast Center is - like more and more landmark metal buildings of the 21st Century - a green building and environmentally friendly.

"It's very sensitive. Whether it's using waterless urinals to decrease the amount of water usage or the amount of glass for light, more natural light in, therefore less electricity. It was also designed post- 9-11, so it is a stunning, secure and safe steel building," William Handkowsky, president and CEO of Liberty Property Trust, said.