The operatic repertory composed between the death of Mozart, in 1791, and the consecration of Rossini, around 1815, is one of the less known to professional musicians of our day and one of the less performed in modern opera houses. A period of deep transformation, in which social, political and economical changes lead to significant innovations in the world of Italian opera and its management as well, establishing new methods and techniques in music composition, with a growing role played by conventions and formulas. Starting from a famous essay by Philip Gossett, this research investigates the evolution of a specific form within the operatic world - the overture - allowing to focus on music issues rather than on the libretti. After a historical recognition on composers and titles that were actually performed in major Italian opera houses during the chosen period, and on the theoretical background provided by composition treatises of the second half of the 18th and early 19th centuries, a corpus of about one hundred thirty overtures by thirty-seven composers is analysed with a double-eyed look -both historical and modern-, in search of recurring patterns and structures, but also of personal solutions and novelties. Comparative study proves that the overture went through a much larger variety of possibilities than its usual description -both in ancient and modern sources- as a "sonata form without development" allows to understand: although forms not related to the sonata are rare, a certain amount of choices were available (number of themes, transition paths, development, crescendo, etc.). While carrying out a much more specific and detailed morphology of the overture, tracing its evolution through some twenty-five years also allows re-establishing historical truth over legendary tools such as the Rossini-crescendo, and to reconstruct the "common language" of Italian opera at the time, making a better understanding of the contributions of each composer possible. This should lead to a new comprehension of authorship, freed from the modern attitude of "genius-at-work", and re-inserted in its historical context of a musical res publica whose forms, tonal paths, compositional formulas, and orchestral solutions, were still common to all its citizens.