When did the Romantic Period in music begin? The generally accepted date is 1830, including by scholars who proclaim Schubert, who died in 1828, to be a Romantic composer. The fact is that while we like to assign firm demarcation points, music, like life, evolves naturally, at fits and starts. There is ultimately no correct answer (but, for what it’s worth, mine is below).
As soon as the Classical rule book had been established, composers began tearing it down. Beethoven threw multiple stones at the Classical edifice, beginning with his Eroica and no more so than his Sixth Symphony, named “Pastoral,” reflecting Beethoven’s attempt to score nature as a metaphor for human, if not his personal, emotions. The desire to connect artist to audience through emotional, rather than spiritual or academic force (but with a healthy dose of politics) is what defines the Romantic Period across art. Most scholars agree that the concept of Romanticism originated with the German poet, playwright, novelist, scientist, statesman, theatre critic, and all round good guy, Johann Wolfgang von Goethe. Fully beyond my brief here, Goethe simply exploded onto the scene in the latter part of the 18th century (he was born a year before Bach died) and has simply remained there. Indelible as any artist or scholar in history. His Faust would become one of the prime inspirations (and one would argue the prime symbol) of the Romantic movement in art.
But what is Romanticism? Since a picture is worth 1,000 words, in fine art, I think first of Eugene Delacroix in France (Liberty Leading the People from 1830):

But I also think about the visionary Francisco Goya in Spain (The Third of May from 1814):

And, of course, the supreme Romantic, J.M.W. Turner in England (The Slave Ship from 1840):

In literature and poetry, William Blake, Lord Byron and Percy Shelley are the architypes for me, along with the Bronte sisters, Victor Hugo, Alexandre Dumas, Stendhal and a host of other 19th century greats.
In the end, it doesn’t matter if Beethoven was a Romantic or a Classicist–his influence was profoundly felt in the Romantic Period even if he remained at his core a Classicist in structure. Schubert too paved the way, most notably by elongating the standard eight-bar theme, which signaled to composers that anything and everything was possible—there were no rules.
In addition to throwing out many of the rules that had constrained composition, Romantic composers looked to new sounds, produced using new techniques on existing instruments or by introducing new instruments. As we approach the 20th century, modern instruments emerge—and they are universally bigger and louder than their predecessors. The size and scale of music similarly grew. Orchestras, which were about 30 strong in Beethoven’s day, grew to more than 100. Operas too became bigger and grander—and increasingly took on highly charged political content. They also grew longer—Wagner was routinely writing more than 4 hours of music for his operas (which means a performance time of over 6 hours).
The Romantic Period also saw the birth new musical forms. The Classical Period gave us the symphony; the Romantic Period saw the rise of smaller forms such the etude, the nocturne, the prelude, and the rhapsody. Programmatic music—the setting of music to tell a narrative story without words—also evolved during this period. Composers increasingly drew on nationalistic sounds, celebrating their own national identity or, alternatively, introducing “foreign” sounds into their music. And the borders of the Western musical world grew, bringing Russia, Eastern Europe, and Scandinavia into the front ranks. Romantic composers, coming somewhat later to the party of human emotion than their counterparts in fine art and literature, drew inspiration from legends and folk tales, using an increasing expanded harmonic vocabulary greater exploit the full chromatic scale—with Beethoven’s late quartets pointing the way forward.
Classical Period composers had intentionally simplified harmony, drawing back from Bach’s complexities to revel in the supreme order of the 1-3-5 chords (think again about the final movement of Beethoven’s Fifth Symphony). Romantics, on the hunt for new and surprising sounds, threw out these artificial limitations, fighting against the entire concept of a fixed key. Thinking back to Pythagoras and his 12 tones, the 7 tones of a musical scale are played on the white keys on a piano, while the five chromatic notes are represented by the five black keys within those 7 white keys. Composers over the centuries had used chromatic notes for a variety of purposes, most notably in the creation of minor scales. Chromatic tones were also used to modulate to a new key without actually changing the key signature (a trick used by Bach and Mozart well before becoming more popular in the Romantic Period). But Romantics began using chromatic tones with increasing frequency to create new harmonics, in particular the diminished seventh. (Note: The Beatles, solo or together, loved a diminished seventh. Harrison’s Blue Jay Way is full of them—listen to the final chord in the line “Now they’ve lost themselves instead”):
The Beatles, Blue Jay Way:
By the end of the Romantic Period, the use (and some would say the overuse) of chromatic tones fully destabilized the rule of tonality in Western music—but that is a story for another time.
In sum, the way I think about Romantic music is like this. I love going to big old movie theaters, like the Uptown Theatre in DC. The lights dim, the previews start and you think, wow, that’s a huge screen. But then the lights go fully out, the curtain recedes, and the full radiance of that cinemascope screen is finally revealed. That’s Romantic music—nothing less than the full monty.
The Romantic Period is notable for opening up a schism in music, notably within the Germanic school. Composers like Felix Mendelssohn considered Beethoven to be an unsurpassable peak in music history, pointing to his symphonies as the final and best musical statement. These “conservatives”—notably Robert and Clara Schumann and Johannes Brahms—sought to continue in Beethoven’s footsteps—so much so that Brahms’ First Symphony is often referred to, derisively in my view, as Beethoven’s Tenth. This slavish adherence to replicating the sound of peak Beethoven led inexorably to a musical dead end and, as beautiful as some of this music no doubt is, these composers ignored the central theory of music history: Everything evolves. These Romantic composers remain, wrongly in my view, at the forefront of the Romantic repertoire.
Contesting these conservatives were the Romantic “progressives,” led by the Hungarian virtuoso pianist and composer Franz Liszt and his son-in-law Richard Wagner. These progressives also revered the late great Beethoven, but were inspired as much by his late quartets as anything else. Seeing the possibilities of an expanded emotional palette made possible through the increased use of chromatic harmony, dissonance, and elongated time-scales, these composers saw Beethoven as pointing the way forward. This, in my view, is the true Romantic Period and the one we will largely trace here.
But we have 70 years to find the apex of Romantic music; so let’s start at the beginning. Where did the Romantic Period begin? I will go out on a limb and give you an exact date: December 5, 1830. And I will give you a place: the Conservatorie National Superieur de Musique et de Danse de Paris. And I will name the work that started it all: Hector Berlioz’s Symphony Fantastique: An Episode in the Life of an Artist, in Five Parts. How’s that for specific?
By the way, the theatre is still standing:

Pay your respects the next time you’re in Paris. This is where one of the high water marks in music history was midwifed.