Juventus bag Bonucci and Martinez
Both players have signed a five-year contract, Juventus said in a statement.
Bonucci, part of Italy's ill-fated World Cup squad and a replacement at Juve for the departed Fabio Cannavaro, cost 15.5 million euros and Uruguayan Martinez a further 12 million.
Twice European Cup winners Juve suffered one of their worst Serie A seasons last term when they finished seventh.
New coach Luigi Del Neri favours a return to a 4-4-2 system after previous bosses Ciro Ferrara and Alberto Zaccheroni dabbled with other formations last season.
Juve, who also have a new president in Andrea Agnelli and sporting director in Beppe Marotta, are pinning their hopes on largely Italian talent with winger Simone Pepe and goalkeeper Marco Storari already arriving in this transfer window.