The Rams have found their center. Los Angeles is signing veteran John Sullivan, a source tells Ian Rapoport of NFL.com (on Twitter). 
The Rams cut former starting center Tim Barnes last month, leaving them without a quality option in the middle. Now, new head coach Sean McVay has brought in Sullivan, a player that he knows fairly well. Last season, the two were together in Washington where Sullivan mostly served as a backup to Spencer Long. Before riding the pine in D.C., Sullivan was the Vikings’ starter for many years.
It’s hard to quantify a center’s performance, but Sullivan was highly regarded by the advanced metrics at Pro Football Focus for his work from 2011 through 2014. Sullivan’s strongest seasons placed him comfortably in the top ten. Even in 2014, a down year by his previous standards, he was still an above average starter, per PFF.
Perhaps more importantly, Sullivan anchored the offensive line for some of Adrian Peterson’s best years in Minnesota. He also offers familiarity with McVay’s offensive system, which should be valuable for this young Rams team.