"It's a big club with big ambitions," Keita said. "This offer has been on the table for three months so I've had the time to reflect and make a well thought out decision.
"With Barcelona I won a lot of trophies but I'm still hungry to win some more wearing this shirt.
"I will bring my experience, especially in the Champions League, even though there are a lot of strong players like Totti and Gervinho.
"I've already seen Roma play and it seems to me that they are a great team, you don't come second in the League by chance.
"I hope to give my contribution in terms of goals and assists in order to make the fans happy."
For the big stories and the banter follow us on Twitter: @tribalfootball