The coal and steel production was key in the post-war rebuilding of the European economy. However, after WWII, Germany still had the technological knowledge and experience to quickly regain its pre-war position as the dominant economic force in Europe. In response to this ‘problem’, the political leaders of six Western European countries founded the European Coal and Steel Community or ECSC, which they hoped would provide a common legal framework for the coal and steel industry. When the ECSC was founded, all six founding countries of the ECSC produced steel and all but two also produced substantial quantities of coal. However, there were considerable differences in the ‘regional concentration’ of the coal and steel companies and before 1952 (the first year of the ECSC), a (relatively) small geographical area was responsible for more than 90 % of both the European coal and steel production. We have then looked at how the relative importance of this ‘industrial triangle’ in the total coal and steel production of the ECSC has decreased between 1952 and 1967 and we discuss the different causes of this decrease. More specifically, we show how the importance of the so-called ‘coastal steelworks’ has increased between 1952 and 1967.