Emirates club welcome second new defender.
Arsenal have agreed an £8million transfer fee for defender Per Mertesacker with Werder Bremen.
The 26-year-old will sign a long-term contract once the formal registration processes are complete.
The Germany international has played 75 times for his country and helped his them to the semi-finals of the 2006 and 2010 World Cups and the final of the 2008 European Championship.
The 6ft 6in centre-back has significant experience for his club at domestic and European level.
He has played eight seasons in the German top flight – five with Werder Bremen and three with Hannover 96 – making 221 league appearances in total and finding the net on 19 occasions.
The former Bremen captain also played 53 times in Europe for the club, including the 2009 Europa League Final.
He will now be expected to form a formidable partnership with Thomas Vermaelen at the heart of the Gunners defence.
Mertesacker becomes Arsenal’s second defensive signing of the day, following the £6.2million arrival of Andre Santos from Fenerbahce.
The Gunners are also working extremely hard to sign a midfielder, with Yann M’Vila and Yoann Gorcuff on the radar, before tonight’s 11pm deadline.