Why did Beethoven's Eroica unsettle its first listeners?

Because it asked for more than a symphony was supposed to give. The Eroica, composed mainly in 1803-1804, broke boundaries in form, length, harmony and emotional content, and is widely seen as a landmark between the Classical and the Romantic eras. A typical performance lasts 45 to 55 minutes.

It begins with two loud chords from the whole orchestra, where Beethoven's first two symphonies opened with slow introductions. Its first movement includes a 32-bar outburst of crashing dissonant chords; Beethoven reportedly lost the beat conducting it, and the players had to stop and go back. The second movement is a funeral march. The scherzo's trio features three horns, the first time that had happened in a symphony. And the finale, which in earlier symphonies was a quick, breezy conclusion, is here a lengthy set of variations and a fugue.

At the first public performance on 7 April 1805, reviews were decidedly mixed. One correspondent reported that to the public the symphony was too difficult and too long. Two years later a reviewer called it the greatest, most original and most interesting of all symphonies.

Then there is the story behind the title. Beethoven had originally dedicated it to Napoleon, whom he believed embodied the ideals of the French Revolution. In autumn 1804 he withdrew the dedication, lest it cost him the fee from a noble patron. His secretary Ferdinand Ries told a more dramatic version: on hearing that Bonaparte had declared himself Emperor, Beethoven tore the title page in half.