 In the summer of 2015, Hungary started building a 4m high fence along its 175 km border to neighbouring Serbia to keep out the tens of thousands illegal immigrants from the Middle East and migrants trying to reach the European Union.The border was sealed on 15 September 2015 and the fence was the following day attacked by refugees and defended by riot police.With the Hungary-Serbia border closed, migrants then started heading to Croatia, but as Croatia led the migrants to the Hungary-Croatia border, Hungary then started the construction of a second fence along its border with Croatia on 18 September 2015.