Some arrived at 7am on Thursday, three hours before the start of the funeral at Basilica di Santa Croce.
The hearse carrying Astori’s body was greeted by loud applause and shouts of his name and “grande capitano” (great captain).
The square then fell silent for a few minutes, while many raised Fiorentina scarves and banners in the air.
Astori’s family arrived along with the hearse, including his partner, Francesca Fioretti, and their two-year-old daughter, Vittoria.
Earlier, the Fiorentina players were met by applause when they arrived on foot, led by midfielder Milan Badelj.
The Croatia international read out a message on behalf of the club during the service, which was broadcast to the crowd outside.
“You are the brother or the son that everyone would have wanted to have,” Badelj said.
“Your parents didn’t make any mistake with you, not even the tiniest bit. You’re not like others, you are football, the real one, the pure one of children.
“Our thoughts go out to your mother and your father, to your brothers, to Francesca and to Princess Vicky. You were a man with a capital M and we will tell her. You are the light for all of us.”
Many other dignitaries and former teammates were also present, including Giuseppe Rossi, who plays for Genoa, and Borja Valero and Matias Vecino, who play for Inter Milan.
Juventus defender Giorgio Chiellini, who played with Astori for Italy, was in tears as he arrived with Gianluigi Buffon and other teammates.
-Dailymail