For example, in the 1950s, East Germans were increasingly prohibited from traveling to the western Federal Republic of Germany where they were automatically regarded as citizens according to Exclusive mandate. The Berlin Wall (1961) and fortifications along the Inner German border (1952 onward) were erected by the Communist German Democratic Republic to enforce the policy. When people tried to "defect" from the GDR they were to be shot on sight. Several hundred people were killed along that border in their Republikflucht attempt. Official crossings did exist, but permissions to leave temporarily or permanently were seldom granted. On the other hand, the GDR citizenship of some "inconvenient" East Germans was revoked, and they had to leave their home on short notice against their will. Others, like singer Wolf Biermann, were prohibited from returning to the GDR.