 Complete the following phrase:  During the 1920s the Greek railway network was split between a number of companies  private and public  with the most important being the SPAP Athens  Piraeus  Peloponnese Railways and the SEK Hellenic State Railways. Eventually the SPAP integrated most railways Southern Greece and the SEK those in Northern Greece. Due to the immense ficial and social pressure during the interwar not much railway construction happened. Important construction projects in the 1920s and 1930s include the expansion of the Piraeus-Thissio Railway towards the centre of Athens via a long tunnel, the attempted extension of the Palaiofarsalos  Kalampaka Railway towards Grevena and Kozani and the construction of the Leukothea  Amphipolis railway line. Much of the railway infrastructure was destroyed during the Second World War and the subsequent 