The Gunners keeper will return to Serie A.
Poland's Wojciech Szczesny
The Polish international enjoyed a successful loan spell with the Italian giants last season and is close to finalising his move there despite late interest from Everton.
Wojciech Szczesny - Arsenal
Szczesny will initially join on a season long-long before a purchase obligation of £13.4 million is activated next summer.
The 26-year old joined the Gunners' youth setup in 2006 – making 181 appearances to date – but he has fallen behind Petr Cech in the pecking order and was unlikely to wrestle a first-team spot away from the veteran stopper.
Arsenal's Petr Cech celebrates at the end of the match
David Ospina has further increased competition between the sticks and after a season as the main man at Roma, Szczesny was never likely to settle for a place on the bench.
Arsenal are well covered in the goalkeeping department and if the reported fee is accurate, the sale represents a healthy return for a player surplus to requirements.
Arsene Wenger will be keen to bolster his team ahead of the new campaign, with injuries to Per Mertesacker and Danny Welback a major blow to squad depth.
Manchester United's Marcos Rojo in action with Arsenal's Danny Welbeck