The Colts exercised the fifth-year option on left tackle Anthony Castonzo, league sources told CBSSports.com on Monday.

Castonzo was selected with the 22nd overall pick of the 2011 NFL Draft by the Colts, drafted to protect Peyton Manning's blindside. Thanks to Manning's four neck surgeries, a lost 2011 season and the divorce that followed, he never got a chance to.

Instead Castonzo's been charged with protecting just as valuable an asset, shoring up the blindside of Andrew Luck after the latest franchise quarterback was taken with the No. 1 overall pick in the 2012 NFL Draft.

Castonzo, one of many notable lineman to graduate from Boston College, will receive a salary (guaranteed for injury only) of $7.438 million in 2015 as a result of the Colts picking up his option.