AC Milan have signed Italy defender Leonardo Bonucci from Juventus for a reported 40m euros (£35.1m).
Bonucci, 30, has signed a five-year deal with the 18-time champions, who have spent about £160m this summer.
Milan coach Vincenzo Montella said: "Technically, I think that he and Sergio Ramos are the strongest central defenders in the world."
Meanwhile, Juve completed the signing of full-back Mattia de Sciglio, 24, from Milan for £10.64m.
A statement on their website said: "Juventus are adding a player with versatility, skill and an international pedigree."
Bonucci's move means he becomes the world's most expensive player aged 30 or over, surpassing the £22.5m Roma paid Fiorentina for striker Gabriel Batistuta in 2000.