the mark of the "rinceaux"

a rinceau (plural rinceaux) is a decorative mark consisting of a continuous wavy stemlike motif from which smaller leafy stems or groups of leaves branch out at more or less regular intervals. 

as in this wonderful rustica motif (9th century):

or this lapida monumentale from Pissa (9th century) 

or on the apse of San Clemente Laterano (10th century)

or this Louis XVI frieze ornament (18th century)

or this magnificent iron work on the door of Notre Dame de Paris (12th century)

the trick is to find the mark from which many of these motifs are develped:

 a- greek, b- roman, c- byzantine, d- romanesque, e & f- gothic, g- renaissance, i & h- baroque, j & k- rococo.

what explains the changes?

no one knows exactly, but it definitely comes from the "vision" of that particular epoch. 

where does all this come from? 

everyday life.