The team also signed linebacker Ernie Sims and defensive end Jamaal Anderson while placing linebacker Darry Beckwith on waivers.
"Thanks to the Colts organization we were able to get this done," said Castonzo. "Now I am excited to get into camp and get to work with my teammates. I know there is a lot for me to learn and I am going to do whatever I can to get on the field."
At 6-7, 305 pounds, Castonzo holds the record for career starts at Boston College (54) while earning Associated Press Third-Team All-America honors and First-Team All-ACC accolades. He was also a finalist for the William V. Campbell Trophy and the Lowe's Senior CLASS Award.
Last season, Castonzo served as a team captain and started all 13 games at left tackle. He was part of an offensive line that blocked for a rushing attack that ranked 16th nationally as running back Montel Harris led the conference individually.
As a junior in 2008, Castonzo garnered SI.com All-America honorable mention honors as well as being named a First-Team All-ACC selection. During his freshman season (2007), he supported current Atlanta Falcons quarterback Matt Ryan during his record-setting senior campaign.
A native of Hawthorn Woods, Illinois, Castonzo was a two-way tackle at Fork Union Military Academy in Virginia.
Sims, 6-0, 230 pounds, is a five-year NFL veteran who spent four seasons with the Detroit Lions (2006-09) and the 2010 campaign with the Philadelphia Eagles. In 74 career contests, the Tallahassee, Florida native has totaled 475 tackles (329 solo), 4.5 sacks, one interception, 10 passes defensed, five forced fumbles and three fumble recoveries. He started all 16 contests in his first three seasons in Detroit and in 2007, totaled a career-high 134 tackles while grabbing his first career interception.
In his final season at Florida State (2005), Sims was a semifinalist for the Butkus Award while garnering All-ACC honorable mention honors. He set a career-high with 10 tackles for loss, while registering 2.5 sacks, two interceptions and a fumble recovery that year.
Anderson, 6-6, 289 pounds, was the eighth overall selection by Atlanta in the 2007 NFL Draft. In four seasons with the Falcons, the Little Rock, Arkansas native started in 47 of 60 career contests and tallied 4.5 sacks, nine passes defensed and two forced fumbles.
At Arkansas, Anderson earned First-Team All-SEC accolades while being named to the honorable mention All-America team in his junior season (2006). He led the conference in sacks with 13.5 while contributing with 19.5 tackles for loss.
Castonzo will be available to the media tomorrow, August 3, following the 9:30 a.m. morning practice session.