By Joe Brewin
The duo lined up together at the heart of defence for the first time in the 1-0 victory over Swansea on Saturday, keeping a clean sheet in the process.
With Thomas Vermaelen sidelined for around a month, 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,” said the Frenchman. “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.”
Koscielny understands that keeping a clean sheet in Dortmund could prove vital to the Gunners’ chances of advancing through the Group Stage, and believes there is enough quality in the squad to see the job through.
“We must defend very well and make a clean-sheet more possible,” he said.
“It is very important to defend together. We have the quality and it is in our hands to perform, along with intelligent players who put the effort in on the pitch.
“We have new players who have arrived at the Club, and it is important for us that they can provide some technical creativity in midfield.”Copyright 2017 The Arsenal Football Club plc. Permission to use quotations from this article is granted subject to appropriate credit being given to www.arsenal.com as the source