Fans were pictured in tears but applauding as Astori's coffin was driven past Fiorentina's Stadium ahead of his funeral, which began at 10am local time at the Santa Croce church in Florence.
Astori, who was just 31, was found dead in Fiorentina's team hotel in Udine on Sunday morning, just hours before the club were due to play Udinese in Serie A.
Juventus coach Massimiliano Allegri, goalkeeper Gianluigi Buffon and defender Giorgio Chiellini were seen arriving for Astori's funeral service after flying back from London, where Juve knocked Tottenham out of the Champions League on Wednesday night.
They were joined by Inter Milan manager Luciano Spalletti, former AC Milan striker Filippo Inzaghi, Khouma Babacar as well as the entire Fiorentina team as they paid their respects to Astori, who died following a "sudden illness" on Sunday.
Hundreds of supporters also paid their respects to Astori in Coverciano, just outside Florence on Wednesday where he was laid in repose as Uefa held a minute's silence before all Champions League matches this week.
An autopsy was carried out on Astori a day earlier, with Italian prosecutors opening a culpable homicide case into his death, although chief prosecutor in Udine, Antonio De Nicolo, stressed it was only a formality at this stage.
Cagliari, who have since changed their Twitter name to 'Ciao Davide', said: "To honor the memory and make indelible the memory of David Astori, @acffiorentina and @CagliariCalcio have decided to jointly withdraw the jersey with the number 13. #DA13."
Chelsea coach Antonio Conte, who selected Astori for Italy during his time managing the national side, admitted he had found news of the defender's death "difficult" to take.
"This is a tragedy and it really hurts me," he told Sky Sports ahead of Chelsea's match against Manchester City on Sunday.
"It's very difficult at this moment to find the right words for the family.
"I had him with the national team. He was a great player but especially a fantastic guy. I stay close to his wife, parents and daughter.
"He was only 31 and it's very difficult to explain this situation."