In March 2013, the Arsenal defence was struggling with the partnership of Per Mertesacker and captain Thomas Vermaelen. Vermaelen was in bad form all season, making six defensive errors, the most by any outfield player, and making a defensive error every 373 minutes. Arsene Wenger decided to change the team ahead of the second leg tie against Bayern Munich which included dropping Thomas Vermaelen – the captain – for Laurent Koscielny. Â The pair of Mertesacker and Koscielny kept a clean sheet against Bayern, something no one else could do last season, and have established themselves as Arsenal’s top centre back partnership.
Arsenal are known for allowing a lot of goals and having a bad defence by fans and the media. Â Last year though, Arsenal were actually quite good defensively if you look at the numbers, especially after this partnership formed. Â In 2011-2012, Arsenal were poor defensively finishing the year eighth in goals conceded with 49. Â This year Arsenal had the second best defensive record in the league conceding only 37 goals. Â Once this partnership became the preferred partnership they became very strong defensively conceding only five goals in the last 10 games of the season. Â The reason the partnership works so well is because they cover each others weaknesses and together they become a great partnership.
Per Mertesacker
Strengths
Mertesacker is a very tall, consistent, and experienced player who does not make many mistakes defensively. Â Mertesacker, 28, is a very experienced defender, he has 94 caps for the German National team and made his debut back in 2004. Â Mertesacker has learned from his experience and is very good at reading the game. Â While he doesn’t make the most interceptions (57 interceptions made last season) his reading of the game allows him to help cover his biggest weakness, his severe lack of mobility. Â Mertesacker made the most appearances among defenders for Arsenal last season but only made one defensive error in his 3,028 minutes of playing time. Â Mertesacker’s height, he is 6’6, is something he takes advantage of by winning 68% of his aerial duels last season.
Weaknesses
Mertesacker is probably best known for his biggest weakness which, as mentioned above, is his severe lack of pace and mobility. Mertesacker is very slow, and when he came to Arsenal many wondered if he would be able to adjust to the pace of the Premier League and, in his first season, he did struggle with the speed of the game. Â Mertesacker’s other big weakness is his tackling. Â Last season, Mertesacker completed only 67% of his tackles, making one every 92 minutes.
Time at Arsenal
Mertesacker joined Arsenal on transfer deadline day of 2011 as one of Arsene Wenger’s ‘panic buys’ after their embarrassing 8-2 defeat against Manchester United. Mertesacker had an “okay” first season, starting 21 games, before it ended after he picked up a non-contact ankle injury which ruled him out for the rest of the season. Â Mertesacker was exposed a few more times, making three defensive errors and one every 610 minutes. Â In his second season, Mertesacker seemed to have adjusted more to the Premier League. Â Mertesacker made 34 appearances, 33 of which were starts, and was consistently good and, while his lack of pace was still sometimes exposed, he looked a lot better.
Laurent Koscielny
Strengths
Koscielny is a very fast defender, a good tackler who makes a lot of interceptions, and also has a habit of scoring big goals for Arsenal. His pace allows him to keep up with most strikers, giving him great recovery ability. Â Koscielny is often seen catching up to strikers even after they are behind him and many times just out paces strikers. Â Koscielny completed 83% of his tackles last season and made one every 40 minutes. Â Koscielny uses his pace to help him get to balls other defenders wouldn’t and with that was able to make an interception every 33 minutes. Â Koscielny has scored six league goals for Arsenal, also scoring the last goal of the 2011-2012 and 2012-2013 season, both years getting Arsenal into the Champions League.
Weaknesses
Koscielny sometimes gets caught out of position and has a habit of scoring own goals. Â Koscielny does like to push forward a bit and, while many times he can get back into position with his pace, Koscielny does sometimes get pulled out of position, leaving gaps in the defence. Koscielny is also known for scoring a lot of own goals which has hurt his reputation as an overall defender.
Time at Arsenal
Koscielny joined Arsenal in the summer of 2010 for £8.45m from the French Club Lorient.  Koscielny struggled early on getting sent off twice in his first season, one of which was his competitive debut.  He had an awful moment in the League Cup final where he and Wojciech Szczesney had a miscommunication allowing Birmingham City to score in the 89th minute losing Arsenal the cup and continuing their trophy drought which is still on going.  Koscielny did have his moments though in his debut season putting in an amazing performance against Barcelona.  Koscielny had an up and down 2011-2012 having tough games, like the 4-3 game against Blackburn where he conceded an own goal, but also played well, like against Chelsea on the 5-3, and he also scored the last goal of the season for Arsenal which had them finish above arch rivals Tottenham and got them into the Champions League.  In 2012-2013, Koscielny played very well, once he started playing consistently, and established himself as Arsenal’s top centre back.  Koscielny scored some big goals this season, he scored the equalizer against Manchester City, the second vs Bayern Munich, and once again scored the last goal of the season to put Arsenal above Tottenham and into the Champions League.  Koscielny was also voted as Arsenal’s second best player, behind Santi Cazorla, at the end of the season, by the fans.
The Partnership
Koscielny and Mertesacker have played a full 90 minutes (includes a start where either have been sent off) 32 times since Mertesacker signed for Arsenal. From these 32 Premier League games the team have managed 20 wins (62.5%), five losses (15.6%), and seven draws (21.9%) and have conceded 31 goals.  Last season, the partnership went undefeated, nine wins, five draws, no losses and only conceded ten goals. The partnership works so well because they compliment each over’s weaknesses.  Koscielny can cover for Mertesacker’s lack of pace and his recovery ability allows him to run over to help out if Mertesacker is burnt for pace.  Many times when Koscielny is caught out of position Mertesacker will read where the ball will go and cover the space Koscielny leaves.  Personality wise they also mesh together well with Mertesacker usually the loudest guy on the pitch screaming out directions while Koscielny is occasionally criticised for being too quiet which sometimes leads to some of his own goals and his awful moment against Birmingham. Since Vermaelen was dropped for Koscielny in March, Arsenal have only allowed two goals from open play, one of those was after Koscielny was sent off, and have proved to be very good and were a big reason Arsenal went on that unbeaten run and qualified the Champions League.
Arsenal have been criticised contently in the media for having a weak spine and being bad defensively.  Many people have also said they need a new top class centre back and need to revamp the defence but with this partnership they seem to really have something.  Arsene Wenger is constantly told to spend money and, while he may need another centre back, he doesn’t need to spend £30m on one because why fix something that’s not broken.  Since the beginning of 2012-2013, Arsenal have lost one game with this partnership and, as Arsene Wenger would say, that was under “very special circumstances”.  With this centre back partnership, Arsenal can win trophies and it is possibly a title winning partnership if they can keep their form and Arsenal can continue to build around them.