Barcelona have officially announced their signing of Arsenal centerback and captain Thomas Vermaelen. In his time at Arsenal, Vermaelen made 150 appearances and scored 15 goals, playing in a back line that was at times good and at times extremely porous. He was made captain after the departure of Robin van Persie, but after some poor play he found himself on the bench - and the issue was exacerbated by the increasingly good partnership between Laurent Koscielny and Per Mertesacker. By the end, there simply wasn't room for Vermaelen as anything other than a top-quality backup, and honestly one can't blame the player for not wanting that life.
Arsenal will likely now look for a replacement for Vermaelen to back up the first-choice central defenders. Calum Chambers has impressed there in preseason, but he's also the third-choice right back and probably the backup to Mikel Arteta, so that might be a bit much. It's unlikely someone with similar experience will be interested - but similar ability might be doable. We'll see what happens in the next twenty-two days.