That means the 49ers' plan is falling into place.
We cannot yet know whether the plan will succeed, but at least the team is delivering on it.
Fangio and Roman worked under Harbaugh at Stanford. They were natural choices to become his coordinators. Losing one of them unexpectedly -- either to Stanford, which was hiring a head coach, or to opportunities elsewhere -- could have qualified as a setback.
Fangio's hiring is the 49ers' most significant move of the day and the one Harbaugh must get right.
That seems odd for a 49ers team that has gone through so many offensive coordinators in recent seasons. But with Harbaugh as the head coach, the team's offensive identity is set. Losing Roman to another opportunity -- think Mike McCarthy after the 2005 season and Norv Turner a year later -- would not force a philosophical change upon the team.
What does Fangio bring? Lots of experience at the college and NFL level, familiarity with Harbaugh and a background in the 3-4 defense.
Fangio worked under Dom Capers in Carolina and Houston. In between, he served under the elder Jim Mora with Indianapolis.
The elder Mora's refusal to fire Fangio precipitated his own firing from the Colts.
The situation was unfortunate for all involved. Mora and Fangio wanted veteran players to run a relatively complicated defense, but the Colts were funneling their resources toward the offensive side as they built around Peyton Manning. Colts management thought the team needed to change its defensive approach -- and its coordinator -- to accommodate personnel shortcomings on that side of the ball.
Fangio was out. His time with the Texans also ended poorly.
Under Fangio, the Colts posted respective rankings of 15th, 21st and 29th in yards allowed. The Texans were 16th, 31st, 23rd and 31st with Fangio.
Neither team had strong defensive talent. The Texans were an expansion franchise.
Fangio spent the 2006 through 2008 seasons in Baltimore as special assistant to the head coach amid some thought that he might succeed Rex Ryan as coordinator. Fangio coached the Ravens' linebackers in 2009, drawing praise from Brendon Ayanbadejo, before joining Harbaugh at Stanford last season.