I would like to have a look at the Symphony No. 3 of Beethoven; the first one that really broke out of the bounds of the 18th century. It was completed in the summer of 1804. There are a number of stories associated with the symphony, in particular the one that relates how it now has the nickname "Eroica" rather than "Bonaparte". For these, have a look at the Wikipedia article. I'm just going to look at the music.
I talked about the introduction to Beethoven's Symphony No. 1 here with its deceptive opening of cadences in the wrong keys before finally settling into C major. The Symphony No. 3 wastes no time with that, instead opening with two forte blasts in E flat major, the tonic. Then we immediately have one of the main themes:
Here is another example of the fluid, dynamic way Beethoven handles the theme. This passage in winds takes the interval between the second and third notes of the original theme, the G falling to the E flat, and slightly ornaments it with an eighth note, then echoes it in the high winds: