David Aldridge of NBA.com reports:

The Boston Celtics’ expected rebuilding began Thursday when veteran forward Rasheed Wallace officially decided to retire after 15 NBA seasons, a league source said.

Wallace’s retirement had been expected after the Celtics’ seven-game loss to the Lakers in the Finals, but Boston had held out some hope that the 35-year-old would change his mind with a few days’ contemplation.

Wallace signed a three-year, $18.9 million contract with Boston last summer, turning down offers from Orlando and San Antonio after the Celtics made a team-wide push to recruit him, sending Coach Doc Rivers, GM Danny Ainge and forwards Kevin Garnett and Paul Pierce to Wallace’s home to ask him to play in Boston. He left more than $12 million on the table by opting to retire.