Now the Eagles have lost their anchor.
Jackson will miss the rest of the season after tearing a knee ligament in Sunday's win over Denver.
"It's obviously a big loss. He's a good football player," coach Andy Reid said Monday.
Jackson made his 71st consecutive start against the Broncos and had been Philadelphia's only offensive player to play every snap until he got hurt in the first half.
He had an MRI exam on Monday that revealed a torn anterior cruciate ligament in his left knee. It's an injury that sometimes takes a full year for recovery, so Jackson may not be ready for the start of next season.
"I don't want to take anything away from losing Jamaal," Reid said. "But at the same time, we're fortunate enough to have guys that have played in games, and big games, that we can fill in those spots."
Right guard Nick Cole replaced Jackson at center, and Max Jean-Gilles took Cole's spot. Mike McGlynn, a second-year pro who has appeared in three career games, becomes the backup center. Stacy Andrews could compete for the starting right guard spot, though he's been inactive the last six games.
Cole had minor issues adjusting to his new position. He snapped the ball too soon at the Eagles 1, but Donovan McNabb fell on it. He also was too slow making a shotgun snap, causing right tackle Winston Justice to jump offside.
"We're fortunate enough to have Nick here," Reid said. "He is a center. This isn't a new territory for him. It's one that he's had a chance to play before and he and Donovan are on the same page. He can make all the calls, he can do the silent counts, he can do the hard count, he knows all of that stuff. That's not a new area for him."
Cole should benefit from working with McNabb all week in practice. The Eagles (11-4) visit Dallas (10-5) on Sunday with the NFC East title at stake.
"I think for myself and Nick, it will be something which we'll work on all throughout the week, and be able to eliminate that going into a tough week against the Cowboys," McNabb said.
Injuries have plagued the Eagles' offensive line since training camp. The projected starters didn't play a single down together.
Philadelphia revamped its line in the offseason, choosing not to re-sign longtime bookend tackles Tra Thomas and Jon Runyan. Shawn Andrews, a two-time Pro Bowl right guard, was expected to move to right tackle. But he landed on injured reserve with a back injury. Winston Justice has started every game at right tackle instead.
The Eagles acquired two-time Pro Bowl left tackle Jason Peters from Buffalo to replace Thomas. Peters started slow and was bothered by injuries, but has played well recently.
Stacy Andrews, Shawn's brother, was signed to a lucrative free-agent contract, despite coming off ACL surgery. But he's started just two games.
"He keeps getting better with his technique and some of that is sticking his leg in the ground, his surgically repaired leg there," Reid said. "I think he has more trust in that now."
The 29-year-old Jackson signed with the Eagles in 2003 as a rookie free agent out of Delaware State. He became a starter midway through 2005 when Hank Fraley was injured.