Two millennia ago, Aretaeus of Cappadocia, a physician from the first to second century CE, first presented a modern portrayal of the relationship between μανίη (mania) and μελαγχολίη (melancholia). His understanding is reflective of the nineteenth-century German clinician, Emil Kraepelin. I propose that Kraepelin and Aretaeus possess more similarities than differences. They were homologous in research techniques and nosology, with one significant difference in aetiology. Presently, Aretaeus’ classification remains recognized in psychiatry, though with a slight deviation in understanding and under different psychiatric labels. Likewise, Kraepelin’s classifications remain highly influential in current clinical practices. Aretaeus’ De Causis et Signis Diuturnorum Morborum (On the Causes and Symptoms of Chronic Diseases) and Kraepelin’s eighth edition of Psychiatrie: Ein Lehrbuch für Studierende und Ärzte (Psychiatry: A Manual for Students and Physicians) will be examined. By critically analyzing these writers, I intend to illustrate a remarkable continuity in the history of manic-depressive insanity.