abstract: The "Liber de motu" by Gerard of Brussels is one of the most complete and technically advanced treatment of motion of the Middle Ages. The main aim of Gerard is to compute the "velocity" of a body whose parts move with different speed. In one of the theorems of the first book, Gerard introduces a method very similar to that of indivisibles. To my knowledge, this is one of the very few, if not the unique, appearence of the indivisibles method during the Middle Ages.