Birmingham have signed former Wigan defender Steven Caldwell on a free transfer.
The 30-year-old centre-back was out of contract and has signed a two-year deal at St Andrews.
The Scotland international made just 15 appearances last season after joining the Latics on a one-year deal from Burnley.
The former Sunderland man is Birmingham's fifth Bosman signing of the summer after the arrival of Marlon King, Chris Burke, Morgaro Gomis and Adam Rooney.
New Blues boss Chris Hughton is having to work within tight financial constraints as he looks to build a squad capable of securing an immediate return to the Premier League.
Caldwell played alongside his brother Gary at Wigan last term after enjoying a three-and-a-half year spell with Burnley.
The ex-Newcastle trainee has twice won promotion to the Premier League, with Burnley in 2009 and Sunderland in 2005.