Arsenal boss Arsene Wenger says he was not surprised that goalkeeper Petr Cech ended his 11-year spell at Stamford Bridge to join Arsenal.
The 33-year-old decided to leave Chelsea after losing his regular place to goalkeeper Thibaut Courtois at the start of last season.
He will be Arsenal's number one with David Ospina as backup.
Poland's Wojciech Szczesny will spend next season on loan in the Serie A at Roma.
"The deal happened because of the special relationship that Petr Cech had with Roman Abramovich," Wenger told the club's official website.
"He had a promise from him that he could go out, no matter where, at a certain price, and that's why it happened.
"It wasn't a huge surprise for me because they couldn't keep him forever, at 33 years of age, as a No 2.
"Goalkeepers have a special problem in the game. If you have to talk about being No 2, you are in trouble. The goalkeeper will say, 'Yes I want to come but I want to play as well'. It's such a problem, and it was for Barcelona last year.
"They played with one goalkeeper in the Champions League and one goalkeeper in the league. That shows you how much you need two goalkeepers, and how much you need to give them games as well.
"He can help us with the continuity of his performances and can help us to develop our keepers, who are top talents.
"He can strengthen the belief in the team as well because when you sit in the dressing room and look around you, you need some people who can give you confidence."