ALAMEDA, Calif. -- The Oakland Raiders agreed to a two-year contract with free-agent safety Reggie Nelson on Wednesday, according to a person with knowledge of the deal.

The person spoke on condition of anonymity because the contract had not been announced by the Raiders. The signing was first reported by ESPN.

Nelson fills one of the final major holes left on the Raiders this offseason. He will replace Pro Bowler Charles Woodson, who retired after last season, and will give Oakland a proven starter in the secondary.

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The 32-year-old Nelson is coming off his best season, having tied for the NFL lead with eight interceptions last season for Cincinnati. Nelson also had 14 passes defensed and was selected to the first Pro Bowl of his career.

Nelson entered the league as a first-round draft pick by Jacksonville in 2007 when current Raiders coach Jack Del Rio was coach of the Jaguars. After three seasons with Jacksonville, Nelson was traded to Cincinnati before the start of the 2010 season and has spent the past six seasons with the Bengals.

Nelson has 30 interceptions and 82 passes defensed in 138 career games.

Nelson is the latest addition to Oakland's defense as Del Rio and general manager Reggie McKenzie look to upgrade that unit after some struggles last season.

The Raiders had previously signed cornerback Sean Smith and linebacker Bruce Irvin. Oakland also signed pass rusher Aldon Smith to a contract earlier this week but he can't join the team until at least November, after his one-year suspension for violating the league's substance abuse policy ends.