In the twelfth and thirteenth century, framing evolved from a method used simply to divine scenes by the Egyptians and Greeks into the artists carving out a hollow in the actual slab of wood, leaving a raised edge, or frame, behind. Then, the artists painted whatever image they chose on the flat portion of the wood. Framing history is, indeed, full of twists and turns heavily dependent on cultural changes.
When using entire pieces of wood for paintings became too costly, framing evolved once again. Wooden moulding strips were used instead to complete the job and joined at the corners. During the 14th and 15th centuries, framing really expanded its reach. Huge pieces were ornamented in churches and cathedrals around the globe. With the Renaissance period, we saw “wealthy nobles” taking a note from these holy places by placing frames in their homes as a sign of ornamental prosperity.
From that moment, frames started to become portable. Instead of leaving the frames in tombs or positioning heavy wooden frames in Cathedrals, these nobles were sure to allow portability. This was done so the pieces could travel from estate to estate.
Framing as a way of life didn’t rear its head until the beginning to mid 16th century. Instead of frames being produced by artists or highly skilled architects, they were being produced by furniture builders. This shift is largely credited to a flourishing arts trade.
The last great shift in the evolution framing occurred in the 17th century under the rule of Louis XIII of France, as frames became refined during that period. 
Frames became thinner, and, as an addition, started to depict leaves, ribbons and corner designs.
So, there you have it. A craft, and an art, was born over hundreds of years of cultural and historical shifts. Framing history was made.
Source: https://en.wikipedia.org/wiki/Picture_frame
