Italy goalkeeper Gianluigi Buffon and his Juventus teammate Giorgio Chiellini were among those who paid their respects in Florence to the defender who captained his club and played 14 times for his country.
One banner in the crowd read "Ciao captain", another "Our captain forever", and purple smoke from flares to match the colour of Fiorentina's shirts filled the sky.
Applause rang out as Astori's coffin was carried into the Santa Croce basilica as children wearing Fiorentina tracksuits formed a guard of honour.
Milan Badelj, Astori's deputy captain at the club, paid tribute to the player in a homily.
"You were the son and the brother that everyone would like to have," the Croatian said. "Your parents didn't put a foot wrong with you, Davide."
He said everyone who remembered Astori would tell his two-year daughter Vittoria that he had been a man with a capital 'M'.
Buffon and Chiellini dashed back from London where the Turin team dedicated their Champions League victory over Tottenham on Wednesday to Astori.
Chiellini said after the match: "He is on our minds on this day. I cried many times. He was a fantastic player."
Daniele De Rossi, Mario Balotelli and Francesco Totti were among Italy players past and present who came to pay their respects and the entire Fiorentina team, dressed in sober dark suits and ties, attended.
Astori was found dead in a hotel room in Udine on Sunday ahead of Fiorentina's Serie A match against Udinese. All matches were postponed in the wake of the discovery.
A post-mortem examination has found he most likely died from a cardiac arrest linked to the slowing of his heart rate.
He will be buried near his home city of Bergamo in northern Italy.
Fiorentina and Astori's former club Cagliari have said they will retire his number 13 shirt in his honour.
There are likely to be more emotional scenes when Fiorentina play their first game since the tragedy when they face Benevento at home on Sunday.
All photos by Filippo Monteforte for AFP.