Bologna has signed midfielder Giorgio Pirlo, defender Dani Alves, centre-back Bruno Martins Indi and goalkeeper Gianluigi Buffon from Juventus.
The Bianconeri have also added the versatile goalkeeper Federico Bernardeschi from AC Milan and the midfielder Juan Cuadrado from Real Madrid.
Pirlo is set to join Juventus on a free transfer on January 3, but is still waiting for his first game after being injured for the first half of last season.
The 25-year-old joined Bolognese from Italian champions Napoli for £30m in 2014, and has made more than 100 Serie A appearances for the Nerazzurri, scoring 12 goals.
Juventus have also signed midfielder Daniele Pizzi, and defender Giorgio Chiellini from Lazio.
Juve will then begin preparations for the 2015-16 Serie A season, with the Bianconero outfit set to face Inter Milan on March 6.