On January 15, 1919, a tank containing over 2 million gallons of molasses burst, sending a wave of thick fluid through the streets of the North End of Boston. It killed 21 people, drowned several horses and caused substantial structural damage to nearby buildings and the elevated railroad. The failure resulted in a three-year trial in which the court auditor found the operator of the tank liable, but was frustrated by the over 20,000 pages of conflicting testimony from dozens of expert witnesses. This paper covers the conditions of the failure from a structural and metallurgical perspective. It reviews the specifications and design practices of the time, methods used to calculate strength of riveted structures, the fracture evidence in light of today’s understanding of the brittle behavior of materials, and presents the results of finite element analyses of the conditions leading up to and beyond initial fracture. The work includes several photographs from the time, including photos of full-scale static and dynamic tests conducted at Lehigh University to investigate the causes of the fracture. The paper also uses work related to other famous failures, for example, the Titanic, to provide information on the materials used at that time.