why are paintings put in rectangular frames?

verdigris

If paintings were not put in rectangular frames but in triangular or hexagonal or circular frames what difference would this make to the end product?
Would the artist be forced to think differently?When the Romans came to the United Kingdom in the first century AD they brought the idea of right angled buildings with them (the native Celts built circular huts).Did the Romans use rectangular frames for paintings on mainland Europe?

russ_watters

They are easy to build, display, store, etc.

fuzzyfelt

http://wings.buffalo.edu/cas/english...asso_Chair.jpg
Picasso, Still life with Chair Caning, 1912

radou

Probably because paper/canvas is mostly rectangular?

Evo

The Romans didn't paint on canvas. They did some painting on wood, but mostly it was wall frescoes and some decorated items.