In order to answer your question, the question itself needs to
be modified. To correct your thought, the Romantic Period did
not occur specifically during Beethoven's lifetime, so it could
therefore not have happened during his "middle" period. It is
important to understand that when talking about labeling a
period of music is to label a zeitgeist of thought, and because
of that, it is fairly impossible to distinguish a particular
moment or instance in which the shift occurred. That said, with
every musical period there are events which reinforce the
current zeitgeist. This is consistent throughout history. These
events are related to the people that we end up studying in
school; such as Beethoven. Beethoven himself is seen as one of
the strongest (and the most famous) connections between the
Classical period and the Romantic period. However, it is
generally considered that for music, what would become the
Romantic period began to seriously gain momentum in the early
1830's, a few years after Beethoven's deat