Discovery in 1904 of the disorder initially called “marble bones”, then in 1926 more appropriately referred to as “osteopetrosis”, is attributed to Heinrich E. Albers-Schönberg (1865–1921), the first radiologist. He used the new technique of “Röntgenographie” to report in a young man the radiographic hallmarks of this osteopathy. Clinical descriptions of lethal forms of osteopetrosis had apparently been published earlier by others. In 1926, "osteopetrosis" (stony or petrified bones) replaced "marble bone disease" because the skeletal fragility resembled limestone more than marble. In 1936, despite fewer than 80 reported patients, a fundamental defect in hematopoiesis, secondarily impacting the entire skeleton, was hypothesized. By 1938, the signature histopathological finding of osteopetrosis was recognized -- persistence of unresorbed calcified growth plate cartilage. Also, it was apparent that besides lethal autosomal recessive osteopetrosis a less severe form was "handed down directly from generation to generation". In 1965, quantitative, but also qualitative, defects in osteoclasts became apparent. Here, I review the discovery and early understanding of osteopetrosis. Characterization of this disorder commencing at the beginning of the past century would support the aphorism of Sir William Osler (1849–1919):​ “Clinics Are Laboratories;​ Laboratories Of The Highest Order”. As featured in this special issue of Bone, the osteopetroses would prove remarkably informative about the formation and function of the cells responsible for skeletal resorption.