Center Back: Sol Campbell
One of the most, if not the most, controversial free transfer in the football history. Campbell left Tottenham after his contract expired in the summer of 2001 even though he was a product of their academies and the Spurs offered him a new contract which would make the defender the highest-paid player in the history of the club. In a move that provoked various reactions, Campbell decided to join Arsenal as a free agent.
Regarded as one of the best ever English defenders, Campbell went on to win 2 Premier League titles and 2 FA Cups with the Gunners. He joined Kolo Toure, Ashley Cole and Lauren in one of the best club defenses which lead Arsenal to the 2003-2004 Premier League title, with the team not losing once in the league. This earned them the nickname 'The Invincibles'.
Moreover, Campbell scored to give Arsenal the lead in the 2006 Champions League final against Barcelona even though the Catalans were eventually crowned champions. He is one of the only 6 English players to have scored in a Champions League final.
Center Back: Joao Miranda
Atletico Madrid hit the jackpot when they managed to sign Miranda on a free transfer in the summer of 2011. Miranda made a name of his own with his appearances at Sao Paulo and reached his peak during his time at the Spanish Capital.
As a Rojiblanco, Miranda helped his team win their first Spanish Liga title since 1997 in 2014. He was named the best defender of that season along with his teammate Filipe Luis and Real's Sergio Ramos. Apart from this, Miranda won 1 Copa del Rey,1 Spanish Super Cup, 1 Europa League, 1 UEFA Super Cup and he contributed to his team reaching the 2014 Champions League final where Atletico was defeated by rivals Real.
One of his highlighted moments as an Atletico's player was his winning goal against Real Madrid in the 2013 Copa del Rey final. His goal brought to an end the streak of 25 games during which Real remained unbeaten by Atletico.