Battle of Siffin
After the battle ended with Ali's victory, Marwan pledged him allegiance. Ali pardoned him and Marwan left for Syria, where his distant cousin Mu'awiya ibn Abi Sufyan, who refused allegiance to Ali, was governor. Marwan was present alongside Mu'awiya at the Battle of Siffin near Raqqa in 657, which ended in a stalemate with Ali's army and abortive arbitration talks to settle the civil war.