Tony Adams has said that familiarity is the key to a successful centre-back pairing.
The former Gunners captain told the club's official website: "It's the only position where you need familiarity. You need to play with your mate on a regular basis to gain confidence and I think that really worked for Arsenal defensively.
"[Manager Arsene Wenger] left that alone and they gained confidence. It's the fact that they play regularly with each other that they've learnt [about] each other's game.
"I think that's what really helped Koscielny and Mertesacker, that they got to know each other's game. For me, Mertesacker is a zonal defender and Koscielny is a man-to-man marker. They got to know each other's game because they played with each other week in, week out."
Arsenal's strong finish to the season ensured that they secured a place in next season's Champions League.