In the article, the understanding of the phenomenon of the crowd by the writer Guy de Maupassant is analyzed. The characteristics of the spontaneous groups in his works, primarily in the essays “On the Water” (1888), are compared with the later theories of S. Sighele, G. Tarde, G. Le Bon, A. Fournial and P. Rossi. It is substantiated that the lack of references to his publications in the first studies on the psychology of the crowd may be due to the factual identity of many ideas presented in the writer's works and the conceptual foundations of those works that claimed to be scientific in considering the material at the end of the 19th century. Features of Maupassant's likening of the crowd to the water element, the specifics of the reflection in his work of the concept of latent animal instincts in the human psyche, the characteristic mixture of feelings of antipathy and fear of loss of identity experienced by the author to the crowd is described. Particular attention is directed to the disclosure by Maupassant of the infection processes in the spontaneous group, the leveling of personality differences, the loss of self-control, manifestations of a tendency to inappropriate behavior. It is noted that in Maupassant's views on spontaneous groups there are two methodological errors, later made by researchers of the phenomenon - attribution of irrationality to an individual in the crowd as opposed to endowing him with rationality in isolation, as well as the spread of the properties of the crowd throughout the social sphere.