TOPSHOT-SERBIA-HUNGARY-EUROPE-MIGRANTS

TOPSHOT - A girl reacts after receiving tear gas during clashes between migrants and Hungarian anti-riot police at the Hungarian border with Serbia near the town of Horgos on September 16, 2015. Europe's 20-year passport-free Schengen zone appeared to be a risk of crumbling with Germany boosting border controls on parts of its frontier with France as migrants desperate to find a way around Hungary's border fence began crossing into Croatia. With a string of EU countries tightened frontier controls in the face of the unprecedented human influx, the cherished principle of free movement across borders -- a pillar of the European project -- seemed in grave jeopardy. AFP PHOTO / ARMEND NIMANI (Photo by ARMEND NIMANI / AFP) (Photo by ARMEND NIMANI/AFP via Getty Images)