Arsenal have signed defender Riccardo Calafiori from Bologna, to strengthen the best defence in the Premier League. Mikel Arteta’s side had the best defensive record last season, conceding just 29 goals in 38 games, and David Raya won the Golden Glove with 16 clean sheets. Arsenal’s back line is the best in the division, with Ben White, William Saliba and Gabriel Magalhaes proving to be vital figures, and they will now be joined by Calafiori, who is expected to play at left-back. Saliba broke a club record as he played in every single minute of the Premier League campaign. The Frenchman is now…