The Gunners came from a goal down to beat Cologne 3-1 in the Europa League on Thursday, but not before the game was delayed for one hour due to crowd trouble which threatened to mar the game.Arsenal face being charged and fined by UEFA following the crowd trouble that threatened to mar their Europa League clash against Cologne.Kick-off was delayed for an hour after some of the 20,000 German fans broke through security to storm the Emirates Stadium.There were skirmishes with stewards as Cologne supporters tried to gather in the away section. Police responded by locking down the sold-out 60,000-seater arena and thousands of home and visiting fans were kept waiting outside until 7.45pm.Read also: Sanchez snubs Zidane in favour of...The match finally kicked off at 9.05pm with riot police with dogs between the German fans and the pitch. Reinforcements arrived to bolster the initial 110 police deployed at the match.Thousands of Cologne fans were mixed among Arsenal fans all around the stadium.The Bundeliga’s bottom club were only given 3,000 tickets but up to 20,000 fans are estimated to have made the trip for their first European tie in 20 years.Police considered calling off the match. Arsenal head of communications Mark Gonnella said: “The decision to go ahead was the best option and the safest option.”Both Arsenal and FC Cologne face UEFA fines if they are proved to be “negligent” in match preparations or there is “a lack of order or discipline observed inside or around the stadium”. There were initially 110 police at the match but more were drafted in.