Arsenal centre-half Laurent Koscielny has no idea why the Gunners were so easily disposed of last night.

The North London club were thrashed 5-1 by Bayern Munich in the Champions League Round of 16 first leg at the Allianz Arena.

"Yeah. I don't know either [what went wrong]," he told Arsenal.com.

"I think the first half was good - we were deep, like you need to be, and tried not to give them space or opportunities to score. It being 1-1 at half-time was good for us but after we conceded the second goal, I think we needed to stay more compact because we had a second leg at home. When you can win [there], you need to stay together, defend together with all 11 players and keep this.

"Tonight we didn't. Bayern played very well - they have some top-class players who can make the difference in front."

Regarding the defensive capitulation that occurred after Koscielny was subbed off with an injury in the 49th minute, the Frenchman said: "It's difficult because during a game like this against a team like this, you need to play together, to have a good spirit and to push yourself for your teammates.

"When you're sitting on the bench in the second half, it's difficult.

"In the first half we did the job and in the second half with their quality it was more difficult."