I'm not sure exactly what you mean here. The Romantic era followed the Classical, Beethoven being the tipping point. You could read endless arguments from music historians as to why Beethoven belongs...
There are many Periods in Classical Music but the most common are the Baroque(1600s), Classical (1700s-) Romantic (1800s-) Modern( 1900-s) Contemporary( now)
The beginning date is usually given as 1750, at the death of J.S. Bach. That's more just a matter of convenience, though, because there were composers continuing in the Baroque style afterwards, and...
It's normally based on chordal patterns, often with alberti base or pedal base, the name of the piece is often something like 'Sonata number 9 in E flat minor', the instrumental music is normally...