Arsenal seal Mertesacker deal
The Germany defender signed what the club described as "a long-term contract" for an undisclosed fee, believed to be around £8million.
Mertesacker said: "I had a great time at SV Werder Bremen and I'm grateful to the club."
He added: "Moving to London enables me to fulfil a dream and a further step in my career.
"The Premier League has always represented a great challenge for me."
Manager Arsene Wenger told his club's official website, www.arsenal.com: "We are delighted to welcome Per Mertesacker to the club.
"He is a German international with vast experience and strength and is good on the floor and in the air.
"I believe he will be well-suited to the Premier League and a tremendous asset to the team."
Meanwhile, the Arteta deal was thought to be dead after the Gunners had a bid rejected on Wednesday afternoon, with reports suggesting Everton had turned down a part-exchange offer.
But it it appears Arsenal may have bowed to the Toffees' demand for a cash-only offer, meaning they faced a race against time to get everything wrapped up before the 11pm deadline.
Related Arsenal News