Arsenal defender Koscielny welcomes Mertesacker arrival
Koscielny knows the importance of a reliable partner at the back and says Mertesacker can be a perfect fit alongside the Club's other defenders.
"He is a very good defender with a lot of experience," the Frenchman told arsenal.com. "He is a German international and is really important for us on the pitch.
"He is tall which is good for our physical side, and he will help me on the pitch with defensive corners."