Harmony and measure
During Baroque period harmony was established as a structural element of music. Harmonic perception of music affects the nature of melody. Major and minor scales are basically used now and three chords are more significant in each scale. I (tonic), IV (subdominant), V (dominant).
Modern measures were used for first time during 17th century but there were previous attempts to subdivide a piece of music dated from 15th and 16th century (particularly in vihuela and clavier music.
Augmented sixth chord
In music theory, an augmented sixth chord contains the interval of an augmented sixth, usually above its bass tone. This chord has its origins in the Renaissance, further developed in the Baroque, and became a distinctive part of the musical style of the Classical and Romantic periods. The three more common types of augmented sixth chords are usually called Italian 6th, French 6th, and German 6th.
Willi Apel, Harvard dictionary of music, eighth edition, eighth printing.
J S Bach's seal