Arsenal boss Wenger: Why I went against policy signing Mertesacker
"Usually, I look at the quality of the player and not at his size," he told arsenal.com. "Because we play a more technical game, I choose smaller players.
"But he is a calming presence, he has over 70 caps with Germany so he has experience and people forget he is only 26 years old.
"He must get used to the pace of the game. It is an issue because he was surprised by that but overall he has qualities we need in our team.
"He reads well the game, has good communication with the other players and he knows how important it is to communicate. That will play a big part in our season."