OKLAHOMA CITY - Friday is a milestone day for downtown Oklahoma City. Devon employees are now moving into the Devon tower.

Devon chairman Larry Nichols calls the day a milestone. It's been three and a half years since Nichols revealed the concept of the tower.

Back in the summer of 2008, the Devon Tower was merely a conceptual model. The 50-story skyscraper was to be a beacon for the city with an attached glass rotunda.

"We wanted a building that would embrace the city, that would have lots of public features," said Larry Nichols, Executive Chairman at Devon Energy.

More than a year later in October of 2009, construction began. In March, workers poured the foundation.

And the building quickly started going up at the rate of one floor a week. The construction was essentially an around-the-clock operation.

In May, the Devon tower officially became the tallest building in Oklahoma. And in September, workers celebrated the laying the highest beam.

Now from the outside, the building is nearly complete. And inside, the first floors now open for business.

Movers will continue to work here through the weekend and about 80 employees will come to work here on Monday.

On the upper floors of the tower construction is still underway. They will not be complete until next year.