Even if the Greek section of the Iron Curtain Trail is short, cyclists have the opportunity to cycle through the former "ΕπιτηρούμενηΖώνη" ("Surveillance Area"), a highly-militarised area along the Bulgarian-Greek border. During the Cold War, owning land or driving a car in this area was forbidden and passing through this 25 km wide strip of land was only possible upon the presentation of a special military passport. After crossing this former border – where access is of course now allowed – EuroVelo 13 enters Greece near the Roupel fortress, famous for its defence during the German invasion in Greece in April 1941. The route re-enters Greece where Ardas river flows along the Greek - Bulgarian border, passes through the lively village of Petrota, follows along the Evros river and enters Turkey after the town of Kastanies, in the low plains near the confluence of Evros and Ardas rivers.