The constant stream of East Germans fleeing across the Inner German border to West Germany placed great strains on East German-West German relations in the 1950s. East Germany sealed the borders to West Germany in 1952, but people continued to flee from East Berlin to West Berlin. On 13 August 1961, East Germany began building the Berlin Wall around West Berlin to slow the flood of refugees to a trickle, effectively cutting the city in half and making West Berlin an enclave of the Western world in communist territory. The Wall became the symbol of the Cold War and the division of Europe. Shortly afterward, the main border between the two German states was fortified.