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 financial 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 Civil War resulting in much of the post-war era being devoted into rebuilding it. The only noteworthy expansion between 1940 and 1971 was the building of a new railway line connecting Larissa to Volos and the extension of the Thessaloniki – Florina railway line to Ptolemaida and Kozani. Also significant was the extension of EIS towards Kifisia by absorbing a former Attica Railway line.