This article is the seventh in a weekly series on the lawyers and law firms behind the 10 tallest U.S. towers under construction.

The Comcast Innovation and Technology Center—a $1.5 billion, 60-story building under construction at 18th and Arch streets in Philadelphia—is scheduled for completion in early 2018.

The mixed-use project includes Philadelphia's largest-ever office lease as well as a Four Seasons hotel and a complex tunnel project.

Comcast turned to Alan S. Ritterband of Ballard Spahr to negotiate a joint venture agreement on the project with Liberty Property Trust. Ritterband got involved in the project in 2013.

"That's when really [Liberty] started sending around term sheets, and were really starting to negotiate," Ritterband said, "when they really started to structure the deal."

Comcast decided to lease all of the available office space at the tower, Philadelphia's largest single-tenant office lease ever.

"The most challenging thing really has been making sure that all the documents work together, because Comcast is both the tenant and it's part of the [landlord] joint venture," Ritterband said.

"This project is just going to be a home run for the city," Ritterband said. "It's going to bring a lot of highly skilled workers into the city."