At 4:00 a.m. on July 28, 1976 the city of Tangshan, China ceased to exist. A magnitude 7.8 earthquake was generated by a fault that passed through the city and caused 85% of the buildings to collapse or to be so seriously damaged as to be unusable, and the death toll was enormous. The earthquake caused the failures of the electric power system, the water supply system, the sewer system, the telephone and telegraph systems, and radio communications; and the large coal mines and the industries dependent on coal were devastated. The railway and highway bridges collapsed so that the city was isolated from the external world. Before the earthquake Tangshan had 1,000,000 inhabitants and it has been estimated that about one half were killed. Although the building code had seismic design requirements, Tangshan was in a zone requiring no earthquake design. An earthquake disaster requires a large earthquake efficiently close to a large city to produce destructive ground shaking and that the city has buildings not designed to resist earthquakes. The Tangshan disaster met all these requirements and the result was the greatest earthquake disaster in the history of the world. Many countries have cities whose situation is similar to that of pre-earthquake Tangshan, that is, an estimated low probability of being struck by destructive ground shaking and many buildings with low seismic resistance so this report should be of special interest to engineers, architects, and government officials in these seismic countries. The report shows what can happen when an unexpected earthquake strikes an unprepared city and it makes clear the need for earthquake preparedness even if the probability of an earthquake is assumed to be low.