Arsenal have signed Italy defender Riccardo Calafiori from Bologna on what the Premier League club said on Monday was a "long-term contract".
No fee was disclosed, but British media reports said Calafiori, 22, had arrived at the Emirates Stadium on a five-year deal worth £42 million ($54 million) after representing Italy at Euro 2024.
"We welcome Riccardo and his family to Arsenal," said Gunners manager Mikel Arteta. "He is a great signing and gives us huge strength to reinforce our defence.
"Riccardo is a big personality and character, with specific skills which will make us stronger as we push to win major trophies.
"He has already shown great development in recent seasons with his performances for both Bologna and Italy, with his progression and development in the past year being really impressive.
"We're looking forward to working with Riccardo, integrating him into the squad and supporting him in the years to come."
Calafiori becomes Arsenal's second major signing of the summer transfer window after David Raya's loan move from London rivals Brentford was made permanent.
The Gunners will be looking to go one better in the 2024/25 season after finishing runners-up to Premier League champions Manchester City by just two points last term.