Milan loan Zapata from relegated Villarreal
Milan have taken the 25-year-old from Spanish club Villarreal who were relegated from La Liga last season and have brought in former Sweden defender Olof Mellberg.
Zapata, who can play in central defence or at full-back, spent six seasons with Udinese before joining Villarreal, having started his career in his homeland with Deportivo Cali.
The move is an unexpected bonus for Zapata who told Colombian media in May that he was uncertain about his future after a difficult season in La Liga.
Milan have sold Thiago Silva and forward Zlatan Ibrahimovic to Paris Saint-Germain, raising questions about their level of ambition for the coming season.
Central defender Nesta also left at the end of last term to join Montreal Impact after 10 years at the club.
They have, however, signed Italy midfielder Riccardo Montolivo from Fiorentina.
Villarreal's new signing Mellberg, who has 116 caps but is not in Sweden's latest squad announced on Tuesday after telling coach Erik Hamren he was "99 percent certain" he would retire following Euro 2012, had been at Olympiakos for three seasons.