The 23^rd International Geological Congress (IGC) hosted in 1968 in Prague, the largest congress of the IGC since the first held in 1878 in Paris (Ellenberger, 1978), was the only one to be cancelled due to a military occupation. The original planned length of the IGC was for a five-week period. The ten days of scientific symposiums were planned to be held from 19^thAugust until 28^th August. The excursions were planned to be held from 8^th August until 7^th September. The 23^rd IGC, the largest ever planned meeting of geologists in Czechoslovakia, was unfortunately interrupted by the beginning of the Warsaw Pact invasion (on 21^st August 1968) and cancelled by the organisers on 23^rd August. This well-prepared congress by the earth scientists and institutions of Czechoslovakia for the international geological community and the International Union of Geoscientists (IUGS) unfortunately only lasted for a total of five days – a period that for many geologists present would never be forgotten as this historical event unfolded and the IGC organizing committee and council dealt with the consequences.