A Syrian boy smiles after crossing the Greek-Macedonian border near Gevgelija on September 18, 2015. Land routes to northern Europe from the Balkans were all closed for migrants, after Croatia closed their border with Serbia because of the unprecedented human wave.  The crisis, challenging the EU&#039;s humanitarian reputation and its vaunted policy of border mobility, has triggered an extraordinary summit, bringing leaders of the 28-nation bloc together next week.  || CREDIT: NIKOLAY DOYCHINOV - AFP/GETTY IMAGES