agreement in the early 1970s as part of the normalisation of relations between the two German states. Crossing the inner German border The inner German border was never entirely sealed in the fashion of the border between the two Koreas and could be crossed in either direction throughout the Cold War. The post-war agreements on the governance of Berlin specified that the Western Allies were to have access to the city via defined air, road, rail and river corridors. This was mostly respected by the Soviets and East Germans, albeit with periodic interruptions and harassment of travellers. Even during the Berlin Blockade of 1948, supplies could be brought in by air – the famous Berlin Airlift . Before and after the Blockade, Western civilian and military trains, road traffic and barges routinely passed through East Germany en route to Berlin. The border could be crossed legally only through a limited number of air, road, rail and river routes. Foreigners were able to cross East German territory to or from West Berlin, Denmark, Sweden, Poland and Czechoslovakia. However, they had only limited and very tightly controlled access to the rest of East Germany and faced numerous restrictions on travel, accommodation and expenditure. Lengthy inspections caused long delays to traffic at the crossing points. Westerners found crossing the inner German border to be a somewhat disturbing experience; Jan Morris wrote: Crossing points Before 1952, the inner German border could be crossed at almost any point along its length. The fortification of the border resulted in the severing of 32 railway lines, three autobahns, 31 main roads, eight primary roads, about 60 secondary roads and thousands of lanes and cart tracks. The number of crossing points was reduced to three air corridors, three road corridors, two railway lines and two river connections giving transit access to Berlin, plus a handful of additional crossing points for freight traffic. The situation improved somewhat after the initiation of détente in the 1970s. Additional crossings for so-called kleine Grenzverkehr – "small border traffic", essentially meaning West German day trippers – were opened at various locations along the border. By 1982, there were 19 border crossings: six roads, three autobahns, eight railway lines plus the Elbe river and the Mittellandkanal. The largest was at Helmstedt-Marienborn on the Hanover–Berlin autobahn, through which 34.6 million travellers passed between 1985–89. Codenamed Checkpoint Alpha, this was the first of three Allied checkpoints