  The structure, formation and evolution of the Universe were some of the main
topics in the scientific debates during the 17th and 18th centuries in Europe.
They involved novel ideas on the cosmos, which concerned aspects that were not
considered before so emphatically, and which were fundamental for the future
development of astronomy. This paper presents a brief account of several
milestones within the gradual definition of pre-galactic systems: the
historical role of the tradition of the plurality of worlds, the significance
of Descartes, and the introduction of the Milky Way and nebulae in the
discourses around the cosmic structure.
