By Chris Emma–

(CBS) When Vic Fangio arrived at Halas Hall having been named new Bears defensive coordinator, the heralded coach faced humble beginnings.

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San Francisco’s circus that ensued after Jim Harbaugh had run his course brought forth a power play that led to Jim Tomsula being hired as head coach, with Fangio hardly warranting consideration. He went from leading one of the NFL’s dominant defenses to taking over a porous Bears defense that had hit historic lows in 2014.

Joining the Bears meant Fangio had to start from scratch in building that identity he instills at each stop — a tough, physical, disciplined defense. To his credit, Fangio made no excuses during his first season with the Bears. There were excuses many to make, as the Bears had personnel more suited for a 4-3 front than Fangio’s 3-4 defense. So he had to plug many square pegs into round holes.

Entering the 2016 season, Fangio’s defense has a new look. It’s a better unit, thanks to a reconstructed front seven. Bears general manager Ryan Pace worked diligently to supply Fangio with a defensive front he can win with.

“It’s that time to kind of get a feel where it all fits together and see what type of defense we’ll be,” Fangio said in early May.

Questions still remain in the secondary, but the Bears made it a clear priority this offseason to upgrade on the defensive line and at linebacker. Come the season opener, it’s possible that the entire Bears base front seven will consist of players brought in by Pace.

The defensive line will be headlined by Eddie Goldman and Akiem Hicks, a stout pair the Bears believe will complement one another. Goldman checks in at 332 pounds, and Hicks is 324 pounds. The two will rotate through the line, giving Fangio various options and looks to use.

Look for plenty of line stunts that allow Goldman and Hicks to create pressure together. Goldman put together a solid rookie season in 2015, improving along the way. Hicks, 26, appears to be getting even better, according to Bears tackle Kyle Long. His versatility is an upgrade on the Bears defense.

“Honestly, that’s all I’ve ever done,” Hicks said. “I’ve always been that tweener kind of defensive lineman — I can play on the outside, I can play on the inside. I can take on a double team, but I can also take an edge and get up field. That’s what’s appetizing to me about this defense, is I get a chance to do that.”

Bears inside linebacker Danny Trevathan had his own way to explain the presence of Hicks.

“He’s a mountain,” Trevathan said. “You can’t move him.”

Success for Fangio’s defense will have to start up front. Goldman and Hicks will be a key to that, and the Bears can hope rookie Jonathan Bullard emerges as a third threat. The Bears like Bullard’s upside and the kind of versatility that’s similar to Hicks. They also have Ego Ferguson, Will Sutton and Mitch Unrein as options to rotate in or potentially start.

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The Bears’ most significant upgrades came at inside linebacker. In 2015, the Bears started five different players at inside linebacker, including a pair of undrafted rookies. Now, they have Trevathan and Jerrell Freeman, who Pro Football Focus proclaimed were the Nos. 1 and 3 free agent linebackers available, respectively.

Trevathan and Freeman are ideal fits for inside linebacker in Fangio’s defense. They’ve already clicked together in OTAs.

“We come from hungry backgrounds,” Trevathan said of Freeman. “We’re out here to eat.”

Now, the Bears have two inside linebackers that fit Fangio’s defense and the kind of edge rushers who can disrupt the backfield. When healthy, Pernell McPhee was often dominant in requiring a double team, while Lamarr Houston and Willie Young transitioned from defensive end to lead the Bears in sacks as edge rushers.

The Bears can hope that first-round pick Leonard Floyd beats out their returning sack leaders to win over playing time at edge rusher. Floyd is the Bears’ future on the outside and, for now, a developmental prospect for Fangio.

“We wanted the speed,” Fangio said of Floyd. “Our team speed up front last year was below average. To add somebody with some speed as part of his tool box was something we were intrigued about.”

Competition for reps at outside linebacker will be heated. The Bears will likely work a steady rotation of McPhee, Houston, Young and Floyd, working alongside the stability of Trevathan and Freeman.

Surely, Fangio will work a fluid rotation on the defensive line, too, utilizing the versatility of Goldman and Bullard to create new looks.

When Fangio was leading the 49ers, a talented defense learned how to play hard-nosed football. Some of the NFL’s top defensive players — Patrick Willis, NaVorro Bowman, Aldon Smith and more — created one of the league’s most touted defenses. Fangio’s 49ers front seven was dominating, a reflection of their defensive coordinator.

It took a season of work and then an offseason of changes, but the Bears have made important upgrades for their front seven. They now have a solid mix of talent and depth on the defensive line and at linebacker.

Fangio came faced a humbling situation when he came to Chicago. Now, he can begin forging his defensive identity.

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Chris Emma covers the Bears, Chicago’s sports scene and more for CBSChicago.com. Follow him on Twitter @CEmma670 and like his Facebook page.